Slight bug in publish on Python 3

On [this line](https://github.com/spacetelescope/asv/blob/32c6471679520b7a95361dfde6f538637873191e/asv/commands/publish.py#L109) I was getting a crash because one of my machine's parameters (ram) was an integer (some number in megabytes), while on another machine the ram parameter was a string "8GB".  I'm not sure if it should have just not been an integer in the first place, but I just went with the default that the configuration provided which was the int value.

This resulted in an "unorderable types" error when sorting.