Add a missing period (#687)

Author: johnzhou721

content/contributing/first-time/what/contents.lr

@@ -171,5 +171,5 @@ gutter:
 
 Want to start small? Once you've poked about a bit in the tutorials,
 check out the BeeWare issues marked [\[good first
-issue\]](https://github.com/search?q=user%3Abeeware+label%3A%22good%20first%20issue%22+is%3Aissue+is%3Aopen&type=issues)
+issue\]](https://github.com/search?q=user%3Abeeware+label%3A%22good%20first%20issue%22+is%3Aissue+is%3Aopen&type=issues).