Tweak README.md

[ishida]

• Fix README.md just a little according to the latest mac version IntelliJ IDEA (2017.3.2)

[codecov-io]

Codecov Report

Merging #439 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #439   +/-   ##
=========================================
  Coverage     62.67%   62.67%           
  Complexity     1401     1401           
=========================================
  Files           174      174           
  Lines          5232     5232           
  Branches       1191     1191           
=========================================
  Hits           3279     3279           
  Misses         1442     1442           
  Partials        511      511

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