Bumb xcode version on circleci (#447)

Author: f-moya

.circleci/config.yml

@@ -24,7 +24,7 @@ jobs:
 
   test_macos:
     macos:
-      xcode: "9.0"
+      xcode: "11.3.0"
     steps:
       - checkout
       - run: brew install golang
@@ -44,7 +44,7 @@ jobs:
 
   release_macos:
     macos:
-      xcode: "9.0"
+      xcode: "11.3.0"
     steps:
       - checkout
       - run: pip install awscli