travisci: Cache Homebrew files

.travis.yml

@@ -7,8 +7,11 @@ python:
 - '3.6'
 - '3.5'
 cache:
-- apt
-- pip
+  apt: true
+  pip: true
+  directories:
+  - $HOME/Library/Caches/Homebrew
+  - /usr/local/Homebrew
 env:
   global:
   - PIP_INSTALL="pip3 install"
@@ -51,6 +54,13 @@ matrix:
     - PYTHON_VERSION=3.7.4
     - INSTALL_DEPS="$PIP_INSTALL -r requirements-macos.txt"
   fast_finish: true
+
+before_cache:
+- if [ "${TRAVIS_OS_NAME}" = "osx" ]; then brew cleanup; fi
+# Credit https://discourse.brew.sh/t/best-practice-for-homebrew-on-travis-brew-update-is-5min-to-build-time/5215/9
+# Cache only .git files under "/usr/local/Homebrew" so "brew update" does not take 5min every build
+- if [ "${TRAVIS_OS_NAME}" = "osx" ]; then find /usr/local/Homebrew \! -regex ".+\.git.+" -delete; fi
+
 before_install:
 - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then sudo apt-get update -qq && sudo apt-get
   install -qq $LIBDISCID qt5-default; fi
@@ -60,18 +70,23 @@ before_install:
 - "$INSTALL_DEPS"
 - "$INSTALL_TEST_TOOLS"
 - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then bash scripts/package-osx.sh; fi
+
 script:
 - py.test -v --cov=picard --cov-report xml:coverage.xml
 - isort --check-only --diff --quiet $(git ls-tree -r --name-only $(git rev-parse HEAD) | grep "\\.py$")
+
 after_success:
 - if [ ! -z "${CODACY_PROJECT_TOKEN}" ]; then $CODACY; python-codacy-coverage -r coverage.xml;
   fi
+
 notifications:
   irc: chat.freenode.net#metabrainz
+
 branches:
   only:
   - master
   - /\d\.[0-9x](\.[0-9x])?/
+
 deploy:
   provider: releases
   api_key: