title: Python:TypeError: array([ 1.]) is not JSON serializable
body: <p>I want to convert the python plot in Html.I have taken reference example and I have changed it to convert plot to Html page.Below is my code:</p>
  
  <pre><code>import matplotlib as plta
  plta.use('Agg')
  import matplotlib.pyplot as plt
  import numpy as np
  import mpld3
  
  fig, ax = plt.subplots(subplot_kw=dict(axisbg='#EEEEEE'))
  N = 100
  
  scatter = ax.scatter(np.random.normal(size=N),
                       np.random.normal(size=N),
                       c=np.random.random(size=N),
                       s=1000 * np.random.random(size=N),
                       alpha=0.3,
                       cmap=plt.cm.jet)
  
  ax.grid(color='white', linestyle='solid')
  ax.set_title("Scatter Plot (with tooltips!)", size=20)
  
  labels = ['point {0}'.format(i + 1) for i in range(N)]
  tooltip = mpld3.plugins.PointLabelTooltip(scatter, labels=labels)
  mpld3.plugins.connect(fig, tooltip)
  
  html_graph = mpld3.fig_to_html(fig)
  with open('plot.html', 'w') as the_file:
      the_file.write(html_graph)
  </code></pre>
  
  <p>Now when I run above code it throws the error as below:</p>
  
  <pre><code>/usr/local/lib/python2.7/dist-packages/matplotlib/cbook/deprecation.py:106: MatplotlibDeprecationWarning: The axisbg attribute was deprecated in version 2.0. Use facecolor instead.
    warnings.warn(message, mplDeprecation, stacklevel=1)
  Traceback (most recent call last):
    File "d3tool.py", line 24, in &lt;module&gt;
      html_graph = mpld3.fig_to_html(fig)
    File "/usr/local/lib/python2.7/dist-packages/mpld3/_display.py", line 251, in fig_to_html
      figure_json=json.dumps(figure_json, cls=NumpyEncoder),
    File "/usr/lib/python2.7/json/__init__.py", line 250, in dumps
      sort_keys=sort_keys, **kw).encode(obj)
    File "/usr/lib/python2.7/json/encoder.py", line 207, in encode
      chunks = self.iterencode(o, _one_shot=True)
    File "/usr/lib/python2.7/json/encoder.py", line 270, in iterencode
      return _iterencode(o, 0)
    File "/usr/local/lib/python2.7/dist-packages/mpld3/_display.py", line 138, in default
      return json.JSONEncoder.default(self, obj)
    File "/usr/lib/python2.7/json/encoder.py", line 184, in default
      raise TypeError(repr(o) + " is not JSON serializable")
  TypeError: array([ 1.]) is not JSON serializable
  </code></pre>
  
  <p>Error occurs on line 24 while calling the fig_to_html() function.Please help me.</p>