Grammar fix in ISSUE_TEMPLATE.md and CONTRIBUTING.md

.github/CONTRIBUTING.md

@@ -16,7 +16,7 @@ wasn’t reported already.
 Each bug report should contain this information:
 
   * Steps to reproduce
-  * What you expected to happened
+  * What you expected to happen
   * What happened instead
 
 In most cases, it is useful to include a **minimal** example (grammar + input)

.github/ISSUE_TEMPLATE.md

@@ -6,7 +6,7 @@ Checklist:
 For bug reports, please include:
 
   * Steps to reproduce
-  * What I expected to happened
+  * What I expected to happen
   * What happened instead
 
 In most cases, it is also useful to include a **minimal** example (grammar + input)