Add missing 'optional' specifier on the fitsopen parameter documentation.
Add missing 'optional' specifier on the fitsopen parameter documentation.

saimn/astropy,mhvk/astropy,funbaker/astropy,pllim/astropy,saimn/astropy,DougBurke/astropy,funbaker/astropy,kelle/astropy,MSeifert04/astropy,stargaser/astropy,bsipocz/astropy,dhomeier/astropy,tbabej/astropy,AustereCuriosity/astropy,astropy/astropy,mhvk/astropy,saimn/astropy,dhomeier/astropy,aleksandr-bakanov/astropy,dhomeier/astropy,astropy/astropy,larrybradley/astropy,dhomeier/astropy,lpsinger/astropy,pllim/astropy,bsipocz/astropy,kelle/astropy,kelle/astropy,StuartLittlefair/astropy,larrybradley/astropy,bsipocz/astropy,tbabej/astropy,stargaser/astropy,joergdietrich/astropy,saimn/astropy,stargaser/astropy,larrybradley/astropy,StuartLittlefair/astropy,aleksandr-bakanov/astropy,aleksandr-bakanov/astropy,astropy/astropy,saimn/astropy,tbabej/astropy,joergdietrich/astropy,MSeifert04/astropy,pllim/astropy,bsipocz/astropy,funbaker/astropy,AustereCuriosity/astropy,lpsinger/astropy,lpsinger/astropy,joergdietrich/astropy,DougBurke/astropy,lpsinger/astropy,pllim/astropy,mhvk/astropy,lpsinger/astropy,larrybradley/astropy,larrybradley/astropy,mhvk/astropy,joergdietrich/astropy,StuartLittlefair/astropy,AustereCuriosity/astropy,pllim/astropy,astropy/astropy,aleksandr-bakanov/astropy,StuartLittlefair/astropy,StuartLittlefair/astropy,astropy/astropy,mhvk/astropy,AustereCuriosity/astropy,joergdietrich/astropy,tbabej/astropy,MSeifert04/astropy,MSeifert04/astropy,kelle/astropy,DougBurke/astropy,tbabej/astropy,dhomeier/astropy,funbaker/astropy,DougBurke/astropy,kelle/astropy,stargaser/astropy,AustereCuriosity/astropy