Fix reference to outdated jwt-go dependency

Earlier today, the dependency `github.com/dgrijalva/jwt-go` dependency was updated to `github.com/dgrijalva/jwt-go/v4`. The docs without this change result in difficult to diagnose type issues, since the types don't mesh up.

Here is the relevant PR that was merged and release for the Go SDK: auth0/go-jwt-middleware#69

articles/quickstart/backend/golang/01-authorization.md

@@ -21,11 +21,11 @@ useCase: quickstart
 
 ### Install dependencies
 
-The [**dgrijalva/jwt-go**](https://github.com/dgrijalva/jwt-go) package can be used to verify incoming JWTs. The [**auth0/go-jwt-middleware**](https://github.com/auth0/go-jwt-middleware) library can be used alongside it to fetch your Auth0 public key and complete the verification process. Finally, we'll use the [**gorilla/mux**](https://github.com/gorilla/mux) package to handle our routes and [**codegangsta/negroni**](https://github.com/urfave/negroni) for HTTP middleware.
+The [**form3tech-oss/jwt-go**](https://github.com/form3tech-oss/jwt-go) package can be used to verify incoming JWTs. The [**auth0/go-jwt-middleware**](https://github.com/auth0/go-jwt-middleware) library can be used alongside it to fetch your Auth0 public key and complete the verification process. Finally, we'll use the [**gorilla/mux**](https://github.com/gorilla/mux) package to handle our routes and [**codegangsta/negroni**](https://github.com/urfave/negroni) for HTTP middleware.
 
 ```bash
 go get -d github.com/auth0/go-jwt-middleware
-go get -d github.com/dgrijalva/jwt-go
+go get -d github.com/form3tech-oss/jwt-go
 go get -d github.com/codegangsta/negroni
 go get -d github.com/gorilla/mux
 ```
@@ -51,7 +51,7 @@ import (
 
 	"github.com/codegangsta/negroni"
 	"github.com/auth0/go-jwt-middleware"
-	"github.com/dgrijalva/jwt-go"
+	"github.com/form3tech-oss/jwt-go"
 	"github.com/gorilla/mux"
 )