Update JWK docs example

Author: Michael Davis

docs/jwk/index.rst

@@ -12,6 +12,7 @@ Verifying token signatures
 .. code:: python
 
     >>> from jose import jwk
+    >>> from jose.utils import base64url_decode
     >>>
     >>> token = "eyJhbGciOiJIUzI1NiIsImtpZCI6IjAxOGMwYWU1LTRkOWItNDcxYi1iZmQ2LWVlZjMxNGJjNzAzNyJ9.SXTigJlzIGEgZGFuZ2Vyb3VzIGJ1c2luZXNzLCBGcm9kbywgZ29pbmcgb3V0IHlvdXIgZG9vci4gWW91IHN0ZXAgb250byB0aGUgcm9hZCwgYW5kIGlmIHlvdSBkb24ndCBrZWVwIHlvdXIgZmVldCwgdGhlcmXigJlzIG5vIGtub3dpbmcgd2hlcmUgeW91IG1pZ2h0IGJlIHN3ZXB0IG9mZiB0by4.s0h6KThzkfBBBkLspW1h84VsJZFTsPPqMDA7g1Md7p0"
     >>> hmac_key = {
@@ -22,6 +23,8 @@ Verifying token signatures
         "k": "hJtXIZ2uSN5kbQfbtTNWbpdmhkV8FJG-Onbc6mxCcYg"
     }
     >>>
-    >>> key = jwk.construct(key_data)
+    >>> key = jwk.construct(hmac_key)
     >>>
-    >>> key.verify(token)
+    >>> message, encoded_sig = token.rsplit('.', 1)
+    >>> decoded_sig = base64url_decode(encoded_sig)
+    >>> key.verify(message, decoded_sig)