Update 6_aspnet_identity.rst (#1796)
Update 6_aspnet_identity.rst (#1796)

Specify DbContext when creating the user database. This resolves the "More than one DbContext was found" when running the command.
chrisowhite/IdentityServer4,MienDev/IdentityServer4,chrisowhite/IdentityServer4,MienDev/IdentityServer4,MienDev/IdentityServer4,IdentityServer/IdentityServer4,IdentityServer/IdentityServer4,IdentityServer/IdentityServer4,MienDev/IdentityServer4,chrisowhite/IdentityServer4,IdentityServer/IdentityServer4