Fix CI for older Node version, update README

[demonmhon]

• Remove *.log and add to .gitignore
• Fix CI that cannot build for Node 4x and 5x
• Minor adjustment on README.md

[codecov-io]

Codecov Report

Merging #16 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #16   +/-   ##
=======================================
  Coverage   98.57%   98.57%           
=======================================
  Files           1        1           
  Lines          70       70           
=======================================
  Hits           69       69           
  Misses          1        1

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