Simplify PULL_REQUEST_TEMPLATE naming MIT license explicitly

The Clip license was the MIT license so far, it's better/easier for
contributors if we name the MIT license explicitly, as there are no
plans to change the Clip library license.

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,8 +1,8 @@
 <!-- Please read the contribution guidelines before submitting a pull request. -->
 <!-- By submitting this pull request, you agree that your contributions are
-     licensed under the Clip license, and agree to future changes to the
-     licensing. -->
+     licensed under the MIT License. -->
 <!-- If you're a first-time contributor, please acknowledge it by
      leaving the statement below. -->
 
-I agree that my contributions are licensed under the Clip license, and agree to future changes to the licensing.
+I agree that my contributions are licensed under the MIT License.
+You can find a copy of this license at https://opensource.org/licenses/MIT