Use master branch for git URL buildpack test

The fix-rewrite-binary-compilation branch does not have cflinuxfs5
in its manifest, causing 'Unsupported stack' when the CF integration
test runs on cflinuxfs5. Use master which always has the current
stack support. The test purpose (verify git URL buildpack deploys
without release YAML pollution) is not branch-specific.

Author: ivanovac

src/php/integration/default_test.go

@@ -94,7 +94,7 @@ func testDefault(platform switchblade.Platform, fixtures string) func(*testing.T
 				}
 
 				deployment, logs, err := platform.Deploy.
-					WithBuildpacks("https://github.com/cloudfoundry/php-buildpack.git#fix-rewrite-binary-compilation").
+					WithBuildpacks("https://github.com/cloudfoundry/php-buildpack.git#master").
 					WithEnv(map[string]string{
 						"BP_DEBUG": "1",
 					}).