Fix set membership test to run faster in python2

[arunkumar-ra]

Fix to this issue: #114
PS. I haven't tested the fix

[codecov-io]

Codecov Report

Merging #115 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #115   +/-   ##
=======================================
  Coverage   98.77%   98.77%           
=======================================
  Files          94       94           
  Lines        6197     6197           
=======================================
  Hits         6121     6121           
  Misses         76       76

Impacted Files	Coverage Δ
pyexcel/internal/sheets/matrix.py	99.04% <100%> (ø)	⬆️

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[chfw]

Thanks for getting it started. I will append the test cases.