Remove semicolon from text/plain content type in example Swagger spec

Author: chrisinmtown

examples/swagger2/helloworld/swagger/helloworld-api.yaml

@@ -13,7 +13,7 @@ paths:
       description: Generates a greeting message.
       operationId: hello.post_greeting
       produces:
-        - text/plain;
+        - text/plain
       responses:
         200:
           description: greeting response