title: Spotipy - Spotify API for Python invalid recommendation request
body: <p>when making a recommendations request such as:</p>
  
  <pre><code>recommend = sp.recommendations(target_energy = 0.5)
  </code></pre>
  
  <p>I get the error:</p>
  
  <pre><code>Traceback (most recent call last):
  File "script.py", line 62, in 
  recommend = sp.recommendations(target_energy = 0.5)
  File "/usr/local/lib/python2.7/dist-packages/spotipy/client.py", line 804, in recommendations
  return self._get('recommendations', **params)
  File "/usr/local/lib/python2.7/dist-packages/spotipy/client.py", line 146, in _get
  return self._internal_call('GET', url, payload, kwargs)
  File "/usr/local/lib/python2.7/dist-packages/spotipy/client.py", line 124, in _internal_call
  headers=r.headers)
  spotipy.client.SpotifyException: http status: 400, code:-1 - https://api.spotify.com/v1/recommendations?target_energy=0.5&amp;limit=20:
  invalid request
  </code></pre>
  
  <p>any particular reason why this is giving an invalid request? I tried consulting the docs but I couldn't find an explenation</p>