travis-ci: fix Perforce install on macOS

The `perforce` and `perforce-server` package were moved from brew [1][2]
to cask [3]. Teach TravisCI the new location.

Perforce updates their binaries without version bumps. That made the
brew install (legitimately!) fail due to checksum mismatches. The
workaround is not necessary anymore as Cask [4] allows to disable the
checksum test for individual formulas.

[1] https://github.com/Homebrew/homebrew-binary/commit/1394e42de04d07445f82f9512627e864ff4ca4c6
[2] https://github.com/Homebrew/homebrew-binary/commit/f8da22d6b8dbcfcfdb2dfa9ac1a5e5d8e05aac2b
[3] https://github.com/caskroom/homebrew-cask/pull/29180
[4] https://caskroom.github.io/Signed-off-by: NLars Schneider <larsxschneider@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

.travis.yml

@@ -75,20 +75,12 @@ before_install:
       popd
       ;;
     osx)
-      brew_force_set_latest_binary_hash () {
-        FORMULA=$1
-        SHA=$(brew fetch --force $FORMULA 2>&1 | grep ^SHA256: | cut -d ' ' -f 2)
-        sed -E -i.bak "s/sha256 \"[0-9a-f]{64}\"/sha256 \"$SHA\"/g" \
-          "$(brew --repository homebrew/homebrew-binary)/$FORMULA.rb"
-      }
       brew update --quiet
-      brew tap homebrew/binary --quiet
-      brew_force_set_latest_binary_hash perforce
-      brew_force_set_latest_binary_hash perforce-server
       # Uncomment this if you want to run perf tests:
       # brew install gnu-time
-      brew install git-lfs perforce-server perforce gettext
+      brew install git-lfs gettext
       brew link --force gettext
+      brew install caskroom/cask/perforce
       ;;
     esac;
     echo "$(tput setaf 6)Perforce Server Version$(tput sgr0)";