honor RUNNER_OS=macOS

Author: Vladimir Kotal

dev/before_install

@@ -46,7 +46,7 @@ if [[ "$TRAVIS_OS_NAME" == "linux" || "$RUNNER_OS" == "Linux" ]]; then
 
 	# for API blueprint verification
 	npm install drafter
-elif [[ "$TRAVIS_OS_NAME" == "osx" ]]; then
+elif [[ "$TRAVIS_OS_NAME" == "osx" || "$RUNNER_OS" == "macOS" ]]; then
 #	brew update
         export HOMEBREW_NO_AUTO_UPDATE=1