Travis-ci - cache macOS app package

[skip AppVeyor]
To avoid rebuild when after_success is cancelled,
so restarting the job can complete the packaging.
Drawback is we need to clear the cache to rebuild
[publish binaries]

.travis.yml

@@ -14,6 +14,7 @@ cache:
   - D2XX
   - site-packages
   - VLC
+  - src/GoldenCheetah.app
 
 env:
   global:

travis/osx/script.sh

@@ -1,7 +1,10 @@
 #!/bin/bash
 set -ev
+# Build only if a package is not already cached
+if [ -z "$(ls -A src/GoldenCheetah.app)" ]; then
 CC=clang CXX=clang++ /usr/local/opt/qt5/bin/qmake -makefile -recursive QMAKE_CXXFLAGS_WARN_ON+="-Wno-unused-private-field -Wno-c++11-narrowing -Wno-deprecated-declarations -Wno-deprecated-register -Wno-nullability-completeness -Wno-sign-compare -Wno-inconsistent-missing-override" QMAKE_CFLAGS_WARN_ON+="-Wno-deprecated-declarations -Wno-sign-compare"
 CC=clang CXX=clang++ make qmake_all
 CC=clang CXX=clang++ make -j4 sub-qwt --silent
 CC=clang CXX=clang++ make -j4 sub-src --silent || CC=clang CXX=clang++ make sub-src
+fi
 exit