add postgres to issue template

.github/ISSUE_TEMPLATE.md

@@ -10,7 +10,7 @@
 - **NodeBB version:** 
 - **NodeBB git hash:** 
 <!-- (to find your git hash, execute `git rev-parse HEAD` from the main NodeBB directory) -->
-- **Database type:** mongo or redis
+- **Database type:** mongo, redis, or postgres
 - **Database version:** 
 <!-- `mongod --version` or `redis-server --version` -->
 - **Exact steps to cause this issue:**