Fixed user email format validation regex.
Fixed user email format validation regex.

See http://guides.rubyonrails.org/security.html#regular-expressions

fdaudens/autotune,voxmedia/autotune,fdaudens/autotune,gellsworth/autotune,voxmedia/autotune,gellsworth/autotune,katieunger/autotune,datadesk/autotune,gellsworth/autotune,katieunger/autotune,fdaudens/autotune,voxmedia/autotune,katieunger/autotune,fdaudens/autotune,datadesk/autotune,datadesk/autotune,katieunger/autotune,gellsworth/autotune,datadesk/autotune,voxmedia/autotune