changelog: fix broken link to contributor

CHANGELOG.md

@@ -12,7 +12,7 @@
 * **Dashboard**: JSON Model under dashboard settings can now be updated & changes saved, [#1429](https://github.com/grafana/grafana/issues/1429), thx [@jereksel](https://github.com/jereksel)
 * **Security**: Fix XSS vulnerabilities in dashboard links [#11813](https://github.com/grafana/grafana/pull/11813)
 * **Singlestat**: Fix "time of last point" shows local time when dashboard timezone set to UTC [#10338](https://github.com/grafana/grafana/issues/10338)
-* **Prometheus**: Add support for passing timeout parameter to Prometheus [#11788](https://github.com/grafana/grafana/pull/11788), thx [@mtanda]
+* **Prometheus**: Add support for passing timeout parameter to Prometheus [#11788](https://github.com/grafana/grafana/pull/11788), thx [@mtanda](https://github.com/mtanda)
 
 # 5.1.3 (2018-05-16)