Update release instructions

Author: José Valim

RELEASE.md

@@ -14,7 +14,7 @@ This document simply outlines the release process:
 
 5. Run `make clean test` to ensure all tests pass from scratch and the CI is green
 
-6. Ensure minimum supported Hex works with new release (check Mix.Tasks.Local.Hex)
+6. Recompile an existing project (for example, Ecto) to ensure manifests can be upgraded
 
 7. Push branch and the new tag