TimeSeries import presents AstropyDeprecationWarning

Importing the TimeSeries object, and probably most other things, results in an AstropyDeprecationWarning relating to the way gzip files are being handled:

WARNING: AstropyDeprecationWarning: astropy.utils.compat.gzip is now deprecated - use the gzip module directly instead [astropy.utils.compat.gzip]

This should be easy to fix by replacing any astropy.utils.compat.gzip imports with just gzip.