Update CONTRIBUTING.md

CONTRIBUTING.md

@@ -7,7 +7,7 @@ Individuals making significant and valuable contributions are given commit-acces
 There are a few basic ground-rules for contributors:
 
 1. **No `--force` pushes** or modifying the Git history in any way.
-1. **Breaking API changes and significant modifications** should be subject to a **pull request** to solicit feedback from other contributors.
+1. **External API changes and significant modifications** should be subject to a **pull request** to solicit feedback from other contributors.
 1. Pull requests to solicit feedback are *encouraged* for any other non-trivial contribution but left to the discretion of the contributor.
 1. Use a non-`master` branch for ongoing work.
 1. Contributors should attempt to adhere to the prevailing code style.