Improve contributing and issue template files

.github/CONTRIBUTING.md

@@ -1,3 +1,3 @@
-As questions at [StackOverflow](http://stackoverflow.com/questions/tagged/redigo+go).
+Ask questions at [StackOverflow](https://stackoverflow.com/questions/ask?tags=go+redis).
 
 Send email to Gary Burd (address in GitHub profile) before doing any work on Redigo.

.github/ISSUE_TEMPLATE.md

@@ -1 +1 @@
-Please ask questions at http://stackoverflow.com/questions/tagged/redigo+go
+Ask questions at https://stackoverflow.com/questions/ask?tags=go+redis