Fix Donate Button on PSF Donate page

From http://python.org/psf/donations/, input[type=image] needed width reset to auto. Also fixed some border box declarations to remove duplication.

Signed-off-by: J. Hogue <j@projectevolution.com>
Merge pull request #121 from proevo/Fix-large-donate-button-ssue-#81

Fix Donate Button on PSF Donate page