ci: Update travis configuration to fix "libintl" loading error

Adapted from the following commits:

* ci: Update travis to fix "libintl" loading error
  See scikit-build/cmake-python-distributions@28b0d4b

* ci: travis update python version from 3.7.4 to 3.7.8
  See scikit-build/cmake-python-distributions@dd85efd

* ci: Tweak cache and before_cache steps
  See scikit-build/cmake-python-distributions@6ec58d7

See scikit-build/cmake-python-distributions#112

Author: jcfr

.travis.yml

@@ -11,20 +11,38 @@ matrix:
     - os: osx
       language: generic
       env:
-        - PYTHON_VERSION=3.7.2
+        - PYTHON_VERSION=3.7.8
 
     - os: osx
       language: generic
       env:
         - PYTHON_VERSION=2.7.15
 
+before_cache:
+  # Cleanup to avoid the cache to grow indefinitely as new package versions are released
+  # see https://stackoverflow.com/questions/39930171/cache-brew-builds-with-travis-ci
+  - brew cleanup
+
 cache:
   directories:
-    - $HOME/.pyenv/versions/3.7.2
+    # Cache downloaded bottles
+    - $HOME/Library/Caches/Homebrew
+    # pyenv
+    - $HOME/.pyenv_cache
+    - $HOME/.pyenv/versions/3.7.8
     - $HOME/.pyenv/versions/2.7.15
+    # scikit-ci-addons
     - $HOME/downloads
 
 before_install:
+  - |
+    # Workaround the following error occuring because python installation is cached but gettext dependency is not
+    #   dyld: Library not loaded: /usr/local/opt/gettext/lib/libintl.8.dylib
+    #     Referenced from: /Users/travis/.pyenv/versions/3.7.2/bin/python
+    #     Reason: Incompatible library version: python requires version 11.0.0 or later, but libintl.8.dylib provides version 10.0.0
+    if [[ "$TRAVIS_OS_NAME" == "osx" && "${PYTHON_VERSION}" == "3.7.8" ]]; then
+      brew install gettext
+    fi
   - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then mkdir $HOME/bin; ln -s $(which pip2) $HOME/bin/pip; ln -s $(which python2) $HOME/bin/python; fi
   - python -m pip install --disable-pip-version-check --upgrade pip
   - pip install -U scikit-ci scikit-ci-addons