Merge branch 'sg/ci-osx-gcc8-fix'

CI build fix.

* sg/ci-osx-gcc8-fix:
  ci: fix GCC install in the Travis CI GCC OSX job

Author: gitster

ci/install-dependencies.sh

@@ -48,6 +48,7 @@ osx-clang|osx-gcc)
 	brew install caskroom/cask/perforce
 	case "$jobname" in
 	osx-gcc)
+		brew link gcc ||
 		brew link gcc@8
 		;;
 	esac