Add Python 2 and 3 build targets to Travis CI

Signed-off-by: Adam Retter <adam.retter@googlemail.com>

.travis.yml

@@ -1,8 +1,5 @@
 sudo: required
 language: node_js
-node_js:
-- 10
-- 12
 git:
   depth: 1
 cache:
@@ -90,9 +87,13 @@ before_install:
       export DISPLAY=:99.0
       Xvfb :99 -screen 0 1024x768x24 > /dev/null 2>&1 &
       echo "XVFB configured"
+      if [[ "$PYTHON" == *python3 ]]; then
+        sudo apt-get -y install python3  
+      fi
     fi
   - curl -o- -L https://yarnpkg.com/install.sh | bash -s -- --version 1.13.0
   - export PATH=$HOME/.yarn/bin:$PATH
+  - python --version
 install:
   - THEIA_SKIP_NPM_PREPARE=1 yarn install --skip-integrity-check
   - npx electron-replace-ffmpeg # re-download library (in case it was cached)
@@ -114,18 +115,40 @@ jobs:
   fast_finish: true
   include:
     - stage: test
+      name: Ubuntu / Node 10 / Python 2
       os: linux
-    - os: osx
+      dist: xenial
+      node_js: 10
+    - stage: test
+      name: Ubuntu / Node 12 / Python 2
+      os: linux
+      dist: xenial
+      node_js: 12
+    - stage: test
+      name: Ubuntu / Node 12 / Python 3 (No Tests!)
+      os: linux
+      dist: xenial
+      node_js: 12
+      env:
+        - PYTHON=/usr/bin/python3
+      before_script:
+        - node --version
+        - $PYTHON --version
+      # no tests, just build
+      script: yarn
+    - name: macOS / Node 12 / Python 2
+      os: osx
       osx_image: xcode11.4
+      node_js: 12
       env: CXX=c++
-      before_script: skip
       script:
         - travis_retry yarn test:theia
-    - os: windows
+    - name: Windows / Node 10 / Python 2
+      os: windows
+      node_js: 10
       env:
         - CXX=c++
         - YARN_GPG=no
-      before_script: skip
       script:
         - travis_retry yarn test:theia
     - stage: deploy