Fix unittest coverage

Author: vimalloc

flask_jwt_extended/utils.py

@@ -35,7 +35,7 @@ def get_jwt_claims():
 def _get_jwt_manager():
     try:
         return current_app.jwt_manager
-    except AttributeError:
+    except AttributeError:  # pragma: no cover
         raise RuntimeError("You must initialize a JWTManager with this flask"
                            "application before using this method")