Save the Homebrew cache on OSX

.travis.yml

@@ -2,6 +2,8 @@ language: generic
 before_install:
     - sh package/linux/travis-decrypt-key
     - if [ "${TRAVIS_OS_NAME}" = "osx" ]; then ( sudo Xvfb :99 -ac -screen 0 1024x768x8; echo ok )& fi
+    - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew update        ; fi
+    - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew install ccache; fi
 script:
     - travis wait 30 bash package/linux/travis-setup.sh
     - mkdir build && cd build
@@ -13,10 +15,6 @@ branches:
   only:
   - master
   - cppgui
-cache:
-  apt: true
-  directories:
-  - "$HOME/cache"
 addons:
   apt:
     sources:
@@ -49,6 +47,10 @@ matrix:
             - CXX=g++-7
             - BOOST_DIR=$HOME/boost_1_63_0
             - DISPLAY=:99.0
+          cache:
+            apt: true
+            directories:
+              - "$HOME/cache"
           after_success:
             - cp slic3r ../
             - LD_LIBRARY_PATH=$WXDIR/lib package/linux/make_archive.sh linux-x64
@@ -61,6 +63,10 @@ matrix:
             - WXVERSION=pkg
             - BOOST_DIR=$HOME/boost_1_63_0
             - DISPLAY=:99.0
+          cache:
+            ccache: true
+          directories:
+            - $HOME/Library/Caches/Homebrew
 env:
   global:
   - secure: eEVRZNMv7FM6jrOU9iAFkDhWxFQ1WtHBEaObImcvtFUxy6vWSt3ehFFeTRouj3uHQAnbvUzziDyvPPm8/95alv5g/du8ML6YzzqKBKfazM0xQ7SF6R2DQL8lfFIp+RSV7T02byEP1f1g7Zva7xH9szIlDcSfU0pXW4KWbkBFMd8=