replace deprecated <center> tag
replace deprecated <center> tag

jrosco/securedrop,jeann2013/securedrop,conorsch/securedrop,jaseg/securedrop,garrettr/securedrop,harlo/securedrop,kelcecil/securedrop,harlo/securedrop,kelcecil/securedrop,jrosco/securedrop,ageis/securedrop,ageis/securedrop,micahflee/securedrop,pwplus/securedrop,GabeIsman/securedrop,micahflee/securedrop,chadmiller/securedrop,GabeIsman/securedrop,ageis/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop,pwplus/securedrop,conorsch/securedrop,ehartsuyker/securedrop,heartsucker/securedrop,heartsucker/securedrop,chadmiller/securedrop,harlo/securedrop,heartsucker/securedrop,jeann2013/securedrop,ehartsuyker/securedrop,jaseg/securedrop,jaseg/securedrop,micahflee/securedrop,jrosco/securedrop,harlo/securedrop,GabeIsman/securedrop,jeann2013/securedrop,chadmiller/securedrop,harlo/securedrop,jeann2013/securedrop,ehartsuyker/securedrop,kelcecil/securedrop,conorsch/securedrop,pwplus/securedrop,harlo/securedrop,kelcecil/securedrop,heartsucker/securedrop,conorsch/securedrop,jaseg/securedrop,pwplus/securedrop,pwplus/securedrop,jaseg/securedrop,pwplus/securedrop,garrettr/securedrop,jeann2013/securedrop,jeann2013/securedrop,ehartsuyker/securedrop,garrettr/securedrop,jrosco/securedrop,heartsucker/securedrop,conorsch/securedrop,ageis/securedrop,jrosco/securedrop,jrosco/securedrop,jaseg/securedrop,chadmiller/securedrop,garrettr/securedrop,GabeIsman/securedrop,chadmiller/securedrop,kelcecil/securedrop,chadmiller/securedrop,GabeIsman/securedrop,micahflee/securedrop,kelcecil/securedrop,GabeIsman/securedrop