Update +1 to 👍

Change comment with a +1 to modern github reaction (👍)

CONTRIBUTING.md

@@ -14,7 +14,7 @@ If you'd like a report a bug or open an issue then please:
 
 1. **Find the correct repository.** ShareLaTeX is split across multiple different repositories, each containing a different service (you can find a list of [all repositories here](https://github.com/sharelatex/sharelatex/blob/master/README.md#other-repositories)). If you know the bug only applies to one service, then please open an issue in that repository. For general bugs and issues that span more than one service, please open an issue in the [sharelatex/sharelatex](https://github.com/sharelatex/sharelatex) repository.
 2. **Check if there is an existing issue.** If there is then please add
-   any more information that you have, or give it a "+1" in the comments.
+   any more information that you have, or give it a 👍.
 
 When submitting an issue please describe the issue as clearly as possible, including how to
 reproduce the bug, which situations it appears in, what you expected to happen, and what actually happens.