PlotlyJSONEncoder doesn't work with simplejson installed

[jayvdb]

Similar to past issues (#415), installation of simplejson breaks plotly.py.

Example failure:

======================================================================
ERROR: test_default_plot_generates_expected_html (test_offline.PlotlyOfflineTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/abuild/rpmbuild/BUILD/plotly.py-3.9.0/plotly/tests/test_core/test_offline/test_offline.py", line 92, in test_default_plot_generates_expected_html
    cls=plotly.utils.PlotlyJSONEncoder)
  File "/usr/lib64/python2.7/site-packages/simplejson/__init__.py", line 419, in dumps
    **kw).encode(obj)
TypeError: __init__() got an unexpected keyword argument 'iterable_as_array'

The build environment can be seen at https://build.opensuse.org/package/show/home:jayvdb:py-wheels/python-plotly

[jonmmease]

Thanks for the report @jayvdb,

Looks like the problem is that we use this snippet in various places in the codebase

from requests.compat import json as _json

Which, in turn, calls

try:
    import simplejson as json
except ImportError:
    import json

This was done in 6634971 in 2016. I believe at the time this was done as a way to support Python < 2.6. Plotly.py no longer supports Python < 2.7 so I think we should just remove this compatibility logic and always use the built-in json module.

[jayvdb]

Bingo that solved the errors in my builds. Submitted a PR.