Remove Xcode 11.3

Remove Xcode 11.3 support because ReactiveSwift 6.3.0 requires Swift 5.2, which is not supported by Xcode 11.3

Author: mluisbrown

.github/workflows/ci.yml

@@ -14,7 +14,6 @@ jobs:
     strategy:
       matrix:
         xcode:
-          - 11.3
           - 11.4
           - 11.5
     steps:
@@ -29,7 +28,6 @@ jobs:
     strategy:
       matrix:
         xcode:
-          - 11.3
           - 11.4
           - 11.5
     steps: