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/logo@2x.png.
• Added import './logo@2x.png'; to App.js.
• Ran npm test. Tests pass.

Created by: vjeux

Accepted. Feel free to merge it once you apply my comments :)

Created by: fson

@vjeux Mind if I merge this without your suggestion? Jest doesn't work with the partial regex at the moment.

Created by: gaearon

@fson

Merged by: fson at 2016-09-10 16:56:43 UTC

Created by: vjeux

Yeah go for it :)