to_flipper doesn't create the right kind of header for flipper

[msyriac]

It seems it needs a pyfits style Header object. If you do

'''
f = a.to_flipper()
f.writeFits(filename)
'''
you get an error.

I'm submitting a PR that fixes this.

[msyriac]

This was due to flipper using pyfits while enlib assuming astropy.io.fits. Flipper has been updated to use astropy.io.fits. However, this still creates errors due to astLib using pyfits. Matt Hilton is pushing an updated astLib to pip soon that uses astropy by default.