Upgrade docker image to Ubuntu focal

See emscripten-core/emsdk#1183

Dockerfile

@@ -1,5 +1,5 @@
 ## Base Image
-FROM buildpack-deps:bionic
+FROM buildpack-deps:focal
 
 ## Package Installation (apt-get)
 RUN EXTRA_CHROME_DEPS="lsb-release fonts-liberation libappindicator3-1" \
@@ -12,7 +12,6 @@ RUN EXTRA_CHROME_DEPS="lsb-release fonts-liberation libappindicator3-1" \
         build-essential \
         cmake \
         openjdk-8-jre-headless `# openjdk-9 is also available, but hits #7232` \
-        python-pip \
         python-setuptools \
         python3 \
         python3-pip \
@@ -34,8 +33,5 @@ RUN EXTRA_CHROME_DEPS="lsb-release fonts-liberation libappindicator3-1" \
     && apt-get clean
 
 ## Package Installation (pip)
-RUN python2 -m pip install --no-cache-dir --upgrade pip \
-    && python2 -m pip install --no-cache-dir flake8==3.7.8
-
 RUN python3 -m pip install --no-cache-dir --upgrade pip \
     && python3 -m pip install --no-cache-dir flake8==3.7.8

README.md

@@ -1,52 +1,52 @@
 # Emscripten CI
 
-The main purpose of this repository is hosting the [Dockerfile](./Dockerfile) 
-for building the Docker image used for the 
-[Emscripten CircleCI build](https://circleci.com/gh/emscripten-core/emscripten).   
+The main purpose of this repository is hosting the [Dockerfile](./Dockerfile)
+for building the Docker image used for the
+[Emscripten CircleCI build](https://circleci.com/gh/emscripten-core/emscripten).
 
-## :whale: Pre-built Docker Image 
-This [Dockerfile](./Dockerfile) allows to build a Docker image, with the tools 
-required for the Emscripten CI build. The image is hosted at 
-[Docker Hub](https://hub.docker.com/r/emscripten/emscripten-ci) and used 
-by the [CircleCI Emscripten Project](https://circleci.com/gh/emscripten-core/emscripten). 
+## :whale: Pre-built Docker Image
+This [Dockerfile](./Dockerfile) allows to build a Docker image, with the tools
+required for the Emscripten CI build. The image is hosted at
+[Docker Hub](https://hub.docker.com/r/emscripten/emscripten-ci) and used
+by the [CircleCI Emscripten Project](https://circleci.com/gh/emscripten-core/emscripten).
 
-The following sections describe the important parts of the [Dockerfile](./Dockerfile). 
+The following sections describe the important parts of the [Dockerfile](./Dockerfile).
 ### Base Image
-The `FROM` instruction sets the base image for the final Docker image. Also, all subsequent instructions are executed using this base image. 
+The `FROM` instruction sets the base image for the final Docker image. Also, all subsequent instructions are executed using this base image.
 
-See [FROM](https://docs.docker.com/engine/reference/builder/#from) (Docker Reference).   
+See [FROM](https://docs.docker.com/engine/reference/builder/#from) (Docker Reference).
 
 ### Package Installation (apt-get)
 Additional packages/tools required by the Emscripten CI build are installed via apt-get using the `RUN` instruction.
 
 It is good practice to execute `apt-get update && apt-get install * && apt-get clean cache` using a single `RUN` instruction, as each docker instruction is creating a new read-only layer. Running `apt-get clean` helps keeping the resulting image size low (which would not be the case if `apt-get install` was executed as a separate `RUN` instruction).
 
-It's recommended to sort the package names alphabetically. For better traceability we created separate package sections for build, docs and test packages.  
+It's recommended to sort the package names alphabetically. For better traceability we created separate package sections for build, docs and test packages.
 
-See [best practices for writing Dockerfiles](https://docs.docker.com/develop/develop-images/dockerfile_best-practices/).   
+See [best practices for writing Dockerfiles](https://docs.docker.com/develop/develop-images/dockerfile_best-practices/).
 
-### Package Installation (pip)  
+### Package Installation (pip)
 
-Pip packages required by the Emscripten CI build are installed in a similar manner as described in the previous section. For example, the `--no-cache-dir` parameter is used in order to keep the size of the final image low. 
+Pip packages required by the Emscripten CI build are installed in a similar manner as described in the previous section. For example, the `--no-cache-dir` parameter is used in order to keep the size of the final image low.
 
 ### Building the image and pushing it to Docker Hub
 
 Use the following commands for updating the `emscripten-ci` pre-built Docker image:
 
-:warning: Write access to the [Docker Hub repository](https://hub.docker.com/r/emscripten/emscripten-ci) is required. 
+:warning: Write access to the [Docker Hub repository](https://hub.docker.com/r/emscripten/emscripten-ci) is required.
 
 1. Clone/pull the latest version of this repository
 
 1. Build docker image locally from the repository root (location of [Dockerfile](/Dockerfile)):
-    
-    `docker build . --tag emscripten/emscripten-ci` 
-  
+
+    `docker build . --tag emscripten/emscripten-ci`
+
 1. Login to your Docker Hub account (if not logged in already):
 
     `docker login`
-      
+
 1. Push docker image to Docker Hub:
-    
+
     `docker push emscripten/emscripten-ci`
-    
-See [Docker CLI reference](https://docs.docker.com/engine/reference/commandline/cli/) for further details.
+
+See [Docker CLI reference](https://docs.docker.com/engine/reference/commandline/cli/) for further details.