redpen: fix trailing comma in test data

test/handler/test_redpen_handler.vader

@@ -47,7 +47,7 @@ Execute(redpen handler should handle errors output):
   \   '        "validator": "Spelling",',
   \   '        "lineNum": 1,',
   \   '        "sentenceStartColumnNum": 0,',
-  \   '        "message": "Found possibly misspelled word \"NeoVim\".",',
+  \   '        "message": "Found possibly misspelled word \"NeoVim\"."',
   \   '      }',
   \   '    ]',
   \   '  }',