Issue with test for rank_size

[mmcky]

@bktaha would you have any time to look into this issue with the rank_size test?

Travis was broken due to the migration to .com from the .org site and QuantEcon.py was using legacy connections -- which has now been fixed.

I'll hold off on issuing a new release until this is fixed.

FAIL: Tests `rank_size` function, which generates rank-size data for
896----------------------------------------------------------------------
897Traceback (most recent call last):
898  File "/home/travis/virtualenv/python3.7.1/lib/python3.7/site-packages/nose/case.py", line 198, in runTest
899    self.test(*self.arg)
900  File "/home/travis/build/QuantEcon/QuantEcon.py/quantecon/tests/test_inequality.py", line 119, in test_rank_size
901    assert_allclose(r_sqval, 1, rtol=1e-4)
902  File "/home/travis/virtualenv/python3.7.1/lib/python3.7/site-packages/numpy/testing/_private/utils.py", line 1528, in assert_allclose
903    verbose=verbose, header=header, equal_nan=equal_nan)
904  File "/home/travis/virtualenv/python3.7.1/lib/python3.7/site-packages/numpy/testing/_private/utils.py", line 840, in assert_array_compare
905    raise AssertionError(msg)
906AssertionError: 
907Not equal to tolerance rtol=0.0001, atol=0
908
909Mismatched elements: 1 / 1 (100%)
910Max absolute difference: 0.00188538
911Max relative difference: 0.00188538
912 x: array(0.998115)
913 y: array(1)

[mmcky]

https://travis-ci.com/github/QuantEcon/QuantEcon.py/jobs/355150820