Create script for shared CI install steps

Intentionally keep conda activate outside script per
conda/conda#7980

.appveyor.yml

@@ -14,16 +14,7 @@ services:
   - docker
 
 install:
-  - wget https://repo.continuum.io/miniconda/Miniconda3-4.6.14-Linux-x86_64.sh
-    --output-document miniconda.sh
-  - bash miniconda.sh -b -p $HOME/miniconda
-  - source $HOME/miniconda/etc/profile.d/conda.sh
-  - hash -r
-  - conda config
-    --set always_yes yes
-    --set changeps1 no
-  - conda env create --quiet --file build/environment.yml
-  - conda list --name manubot
+  - bash ci/install.sh
   - conda activate manubot
 
 test_script:

.travis.yml

@@ -6,18 +6,8 @@ services:
 branches:
   only:
     - master
-before_install:
-  - wget https://repo.continuum.io/miniconda/Miniconda3-4.6.14-Linux-x86_64.sh
-    --output-document miniconda.sh
-  - bash miniconda.sh -b -p $HOME/miniconda
-  - source $HOME/miniconda/etc/profile.d/conda.sh
-  - hash -r
-  - conda config
-    --set always_yes yes
-    --set changeps1 no
 install:
-  - conda env create --quiet --file build/environment.yml
-  - conda list --name manubot
+  - bash ci/install.sh
   - conda activate manubot
 script:
   - bash build/build.sh

ci/install.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+
+## install.sh: run during a Travis CI or AppVeyor build to install the conda environment.
+
+# Set options for extra caution & debugging
+set -o errexit \
+    -o nounset \
+    -o pipefail
+
+wget https://repo.continuum.io/miniconda/Miniconda3-4.6.14-Linux-x86_64.sh
+    --output-document miniconda.sh
+bash miniconda.sh -b -p $HOME/miniconda
+source $HOME/miniconda/etc/profile.d/conda.sh
+hash -r
+conda config
+  --set always_yes yes
+  --set changeps1 no
+conda env create --quiet --file build/environment.yml
+conda list --name manubot