Update 4_javascript_client.rst (#4292)
Update 4_javascript_client.rst (#4292)

added an additional step to maintain consistency with previous tutorial chapters. This would be useful if a learner skips ahead directly to building a JS client after getting the main auth server to work.
IdentityServer/IdentityServer4,IdentityServer/IdentityServer4,MienDev/IdentityServer4,MienDev/IdentityServer4,MienDev/IdentityServer4,IdentityServer/IdentityServer4,MienDev/IdentityServer4,IdentityServer/IdentityServer4