Fix link to merged pull requests

Author: Philippus

README.md

@@ -29,7 +29,7 @@ look like, here are the ones it has created so far:
 
 * [Created pull requests](https://github.com/search?q=author%3Ascala-steward+is%3Apr)
   ([compact](             https://github.com/pulls?q=author%3Ascala-steward+is%3Apr))
-* [Merged pull requests]( https://github.com/search?q=author%3Ascala-steward+is%3Amerged+sort%3Aupdated-desc)
+* [Merged pull requests]( https://github.com/search?q=author%3Ascala-steward+is%3Amerged+sort%3Aupdated-desc&type=pullrequests)
   ([compact](             https://github.com/pulls?q=author%3Ascala-steward+is%3Amerged+sort%3Aupdated-desc))
 
 You can also watch what it is currently doing [here](https://gitstalk.netlify.com/scala-steward).