Any boto version will do

This is for https://github.com/edx/edx-platform/pull/4697 -- a new version of `boto` came out since the last upgrade that was applied to edx-ora2. I've adjusted the requirements to be more flexible. Once this goes in, we'll need to make a new release and update https://github.com/edx/edx-platform/pull/4697 to point to it.