Support string type for commands

Summary:
String type seems to be already supported by codegen, but it was not included in the list for command methods.

Changelog: [Internal]

Reviewed By: JoshuaGross

Differential Revision: D29306740

fbshipit-source-id: 44b267c09f471dc601759ed2f7211a9e0fc1bb90

packages/react-native-codegen/src/parsers/flow/components/commands.js

@@ -76,6 +76,11 @@ function buildCommandSchema(property, types: TypeDeclarationMap) {
           type: 'FloatTypeAnnotation',
         };
         break;
+      case 'StringTypeAnnotation':
+        returnType = {
+          type: 'StringTypeAnnotation',
+        };
+        break;
       default:
         (type: empty);
         throw new Error(