Fix a typo in contributing.md

docs/developers/contributing.md

@@ -6,7 +6,7 @@ New contributions to the library are welcome, but we ask that you please follow
 - Consider whether your changes are useful for all users, or if creating a Chart.js [plugin](plugins.md) would be more appropriate.
 - Check that your code will pass tests and `eslint` code standards. `npm test` will run both the linter and tests for you.
 - Add unit tests and document new functionality (in the `test/` and `docs/` directories respectively).
-- Avoid breaking changes unless there is an upcoming major release, which are infrequent. We encourage people to write plugins for most new advanced features, and care a lot about backwards compatibility.
+- Avoid breaking changes unless there is an upcoming major release, which is infrequent. We encourage people to write plugins for most new advanced features, and care a lot about backwards compatibility.
 - We strongly prefer new methods to be added as private whenever possible. A method can be made private either by making a top-level `function` outside of a class or by prefixing it with `_` and adding `@private` JSDoc if inside a class. Public APIs take considerable time to review and become locked once implemented as we have limited ability to change them without breaking backwards compatibility. Private APIs allow the flexibility to address unforeseen cases.
 
 ## Joining the project