Decode jwt bytes object in Python 3 (#633)

github/MainClass.py

@@ -633,12 +633,17 @@ class GithubIntegration(object):
             "exp": now + 60,
             "iss": self.integration_id
         }
-        return jwt.encode(
+        encrypted = jwt.encode(
             payload,
             key=self.private_key,
             algorithm="RS256"
         )
 
+        if atLeastPython3:
+            encrypted = encrypted.decode('utf-8')
+
+        return encrypted
+
     def get_access_token(self, installation_id, user_id=None):
         """
         Get an access token for the given installation id.
@@ -689,4 +694,4 @@ class GithubIntegration(object):
         raise GithubException.GithubException(
             status=response.status,
             data=response_text
-        )
+        )