Fix link to Contributing guide (#106)

Author: Turnerj

.github/PULL_REQUEST_TEMPLATE.md

@@ -2,5 +2,5 @@
 Thank you good citizen for your hard work!
 
 Please read the contributing guide before raising a pull request.
-https://github.com/RehanSaeed/Schema.NET/blob/master/CONTRIBUTING.md
+https://github.com/RehanSaeed/Schema.NET/blob/master/.github/CONTRIBUTING.md
 -->