chore: more caching on MacOS Travis

.travis.yml

@@ -107,6 +107,13 @@ matrix:
       os: osx
       osx_image: xcode9.2
       env: JOB=build-osx
+      cache:
+        ccache: true
+        directories:
+          - $HOME/Library/Caches/Homebrew
+      before_cache:
+        - brew cleanup
+
     - stage: "macOS, AppImage and Flatpak"
       os: linux
       env: JOB=APPIMAGE

.travis/build-osx.sh

@@ -30,6 +30,7 @@ install_ccache() {
     brew update
     echo "Installing ccache..."
     brew install ccache
+    brew --cache
 }
 
 # Build OSX