Update CONTRIBUTING.md

CONTRIBUTING.md

@@ -2,7 +2,7 @@
 # Stack Overflow
 **Stack Overflow** is a fantastic resource for programmers, with many active users who are usually able to answer questions much quicker than I can. 
 
-[Follow this link](http://stackoverflow.com/questions/ask?tags=reachability%20swift) to ask your question on SO
+[Follow this link](http://stackoverflow.com/questions/ask?tags=reachability-swift) to ask your question on SO
 
 # Raising an issue here