Add missing close quote. (jpadilla#327)

Author: stephenpaulger

docs/usage.rst

@@ -21,7 +21,7 @@ Encoding & Decoding Tokens with RS256 (RSA)
     >>import jwt
     >>private_key = b'-----BEGIN PRIVATE KEY-----\nMIGEAgEAMBAGByqGSM49AgEGBS...'
     >>public_key = b'-----BEGIN PUBLIC KEY-----\nMHYwEAYHKoZIzj0CAQYFK4EEAC...'
-    >>encoded = jwt.encode({'some': 'payload'}, private_key, algorithm='RS256)
+    >>encoded = jwt.encode({'some': 'payload'}, private_key, algorithm='RS256')
     'eyJhbGciOiJIU...'
     >>decoded = jwt.decode(encoded, public_key, algorithms='RS256')
     {'some': 'payload'}