Fix a problem with test_votable_quantity_write()
Fix a problem with test_votable_quantity_write()

Using angstroms with the 'vounit' format raises a UnitsWarning that
suggests angstroms should not be used. This warning causes
test_votable_quantity_write() to fail even though the functionality of
the underlying code is not compromised. Replacing angstroms with
something else allows the test to pass.

dhomeier/astropy,astropy/astropy,astropy/astropy,saimn/astropy,saimn/astropy,StuartLittlefair/astropy,lpsinger/astropy,pllim/astropy,StuartLittlefair/astropy,larrybradley/astropy,pllim/astropy,dhomeier/astropy,dhomeier/astropy,mhvk/astropy,larrybradley/astropy,aleksandr-bakanov/astropy,pllim/astropy,astropy/astropy,StuartLittlefair/astropy,lpsinger/astropy,larrybradley/astropy,dhomeier/astropy,astropy/astropy,larrybradley/astropy,aleksandr-bakanov/astropy,saimn/astropy,dhomeier/astropy,astropy/astropy,mhvk/astropy,aleksandr-bakanov/astropy,saimn/astropy,mhvk/astropy,saimn/astropy,aleksandr-bakanov/astropy,pllim/astropy,lpsinger/astropy,StuartLittlefair/astropy,lpsinger/astropy,mhvk/astropy,lpsinger/astropy,pllim/astropy,StuartLittlefair/astropy,larrybradley/astropy,mhvk/astropy