Config file md5 calculation broken on Windows 7

As reported by @anizami in #1802, the test that checks the calculation of the md5 sum of the config file fails on Windows 7.

https://gist.github.com/anizami/4127d40c8a4cc39ec4c2

Not sure why yet, but wanted to create an issue for this.

While fixing the test would be nice, I don't consider this a high priority or indicative of a serious bug.  The worst that will happen here is that a user with a default astropy 0.3 config file will not have it automatically replaced by an astropy 0.4 config file.  Annoying to be sure, but it shouldn't result in loss of data or config settings etc.