fix deprecation warning about default h5py file mode
fix deprecation warning about default h5py file mode

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