10Gen repo broken on some 32 bit REHL architectures/variants

Oops, accidentally created this issue without a title by misusing [hub](http://hub.github.com/).

Anyway, this PR is a simple fix for the issue mentioned in #32 - my vagrant box reports i386 instead of i686 so the mongo repo wasn't working on CentOS6.4 (it was not getting a URL).  Adding this makes it all work as expected.