Fix mocking assets with special characters in the file path

Created by: fson

The regexes in the Jest moduleNameMapper configs were a bit too strict, causing them to not pick up files with special characters like @ in the file path. Change them to match anything with the correct file extension.

Fixes #579 (closed).

Test plan:

• Created a file named template/src/[email protected].
• Added import './[email protected]'; to App.js.
• Ran npm test. Tests pass.