Update xcode

Author: abraham

.circleci/config.yml

@@ -2,11 +2,10 @@ version: 2
 jobs:
   build:
     macos:
-      xcode: "9.1.0"
+      xcode: "11.3.1"
     steps:
       - checkout
-      - run: brew upgrade npm
-      - run: brew install caskroom/cask/firefox caskroom/cask/google-chrome
+      - run: brew cask install firefox google-chrome
       - run: node --version
       - run: npm --version
       - restore_cache: