Update CONTRIBUTING.md link syntax for style guide (#723)

CONTRIBUTING.md

@@ -21,7 +21,7 @@ Please note that this project is released with a [Contributor Code of Conduct][c
 
 Here are a few things you can do that will increase the likelihood of your pull request being accepted:
 
-- Follow the [style guide][https://standardjs.com/] which is using standard. Any linting errors will be shown when running `npm test`
+- Follow the [style guide](https://standardjs.com/) which is using standard. Any linting errors will be shown when running `npm test`
 - Write and update tests.
 - Keep your change as focused as possible. If there are multiple changes you would like to make that are not dependent upon each other, consider submitting them as separate pull requests.
 - Write a [good commit message](http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html).