Use full qualified URL for contribution guideline

cosmo0920 · cosmo0920 · commit 56b9895e61e9 · 2019-08-08T18:31:55.000+09:00
diff --git a/ISSUE_TEMPLATE.md b/ISSUE_TEMPLATE.md
@@ -1,5 +1,5 @@
 (check apply)
-- [ ] read [the contribution guideline](CONTRIBUTING.md)
+- [ ] read [the contribution guideline](https://github.com/uken/fluent-plugin-elasticsearch/blob/master/CONTRIBUTING.md)
 
 #### Problem
 
