Remove decode in wrong place.
Remove decode in wrong place.

  File "[...]/lib/python3.3/site-packages/requests_oauthlib/oauth1_auth.py", line 70, in __call__
    r.url = to_native_str(r.url)
  File "[...]/lib/python3.3/site-packages/requests_oauthlib/oauth1_auth.py", line 14, in to_native_str
    return string.decode('utf-8')
AttributeError: 'str' object has no attribute 'decode'

Request object have 'url' attribute with 'str' type, not 'bytes' so
decode in this place is wrong.

requests/requests-oauthlib,jayvdb/requests-oauthlib,elafarge/requests-oauthlib,jayvdb/requests-oauthlib,dongguangming/requests-oauthlib,singingwolfboy/requests-oauthlib,lucidbard/requests-oauthlib,gras100/asks-oauthlib,jsfan/requests-oauthlib,abhi931375/requests-oauthlib,sigmavirus24/requests-oauthlib