Update CONTRIBUTING.md

Author: JLJu

CONTRIBUTING.md

@@ -1,3 +1,3 @@
-[Check the code of conduct here](/blob/master/CODE_OF_CONDUCT.md)
+[Check the code of conduct here](/CODE_OF_CONDUCT.md)
 ## Best way of contribution is to find some open issue or bug and fix it!
 [General contribution and contact info](http://www.basicairdata.eu/join/)