Update Types title in CONTRIBUTING.md

Author: slowcheetah

CONTRIBUTING.md

@@ -65,7 +65,7 @@ engine            | how to run tests | base data inherits from    | mandatory ch
 
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-## How to add new TypeScript definitions
+## TypeScript types definitions
 
 - TypeScript definitions should be added to the [`packages/core-js-types/src/base`](./packages/core-js-types/src/base) directory.
 - Our type definitions are built on top of ES6. If any related type is missing in ES6, it must be added to the [`packages/core-js-types/src/base/core-js-types`](./packages/core-js-types/src/base/core-js-types) directory and imported via triple-slash directives in your type definition file.