Removing forcing of tqdm version for python2

[surgan12]

Relates to #766 which mentions problems with installing newer versions of the package due to tqdm==4.19.9.

This forcing was done in #542 due to error mentioned in #541.

The new release tqdm==4.31.1 handles the problem mentioned in #541 and no error appears on downloading.
I hope in the versions following 4.31.1 , tqdm wont regress to the same problem mentioned in #541 .

cc : @vishwakftw @fmassa

[codecov-io]

Codecov Report

Merging #767 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #767   +/-   ##
=======================================
  Coverage   40.31%   40.31%           
=======================================
  Files          29       29           
  Lines        2746     2746           
  Branches      432      432           
=======================================
  Hits         1107     1107           
  Misses       1563     1563           
  Partials       76       76

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[surgan12]

#768 addresses this .