use a fixed version of IPython

[marvinmin]

It should be able to fix the bug of installing from test PyPI.
close #80

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@e56f119). Click here to learn what that means.
The diff coverage is n/a.

@@           Coverage Diff            @@
##             master     #82   +/-   ##
========================================
  Coverage          ?   97.7%           
========================================
  Files             ?       3           
  Lines             ?     261           
  Branches          ?       0           
========================================
  Hits              ?     255           
  Misses            ?       6           
  Partials          ?       0

Flag	Coverage Δ
#unittests	97.7% <ø> (?)

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