Update CONTRIBUTING.md (#664)

fix spelling error/typo in contributing readme

.github/CONTRIBUTING.md

@@ -18,7 +18,7 @@ We want to help bring academic research closer to practitioners and we strive to
 
 * Directory names are undercased and separated by underscores (example: artificial_intelligence)
 * Paper names are undercased and separated by dashes (example: out-of-the-tar-pit.pdf). Use the full title when possible.
-* If your pull request includes a binary file, like a `*.pdf` for example, please still include a link to the source URL in the appropriate subject's folder's README file and highlight it with a :scroll: emojii to show that the directory contains the file itself. Here's an example [pull request](https://github.com/papers-we-love/papers-we-love/pull/366/files).
+* If your pull request includes a binary file, like a `*.pdf` for example, please still include a link to the source URL in the appropriate subject's folder's README file and highlight it with a :scroll: emoji to show that the directory contains the file itself. Here's an example [pull request](https://github.com/papers-we-love/papers-we-love/pull/366/files).
 * After raising [this issue](https://github.com/papers-we-love/papers-we-love/issues/290), it would beneficial to also include the *year* along with the title, link, and description/importance when adding paper(s) to a README.
 * Please rebase all multi-commit branches/PRs into 1 single commit.