docs(readme): fix broken link to CONTRIBUTING.md (#289)

Munter · michael-ciniawsky · commit c1c5a7f07365 · 2018-08-21T14:52:12.000+02:00
diff --git a/README.md b/README.md
@@ -371,7 +371,7 @@ path/to/file.png?e43b20c069c4a01867c31e98cbce33c9
 
 Please take a moment to read our contributing guidelines if you haven't yet done so.
 
-#### [CONTRIBUTING](./.github/CONTRIBUTING)
+#### [CONTRIBUTING](./.github/CONTRIBUTING.md)
 
 ## License
 
