Make test coverage fancy

[vinhlh]

To have 100% code coverage

[codecov]

Codecov Report

Merging #38 into master will increase coverage by 6.45%.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master    #38      +/-   ##
========================================
+ Coverage   93.54%   100%   +6.45%     
========================================
  Files           4      3       -1     
  Lines          31     29       -2     
  Branches        4      3       -1     
========================================
  Hits           29     29              
+ Misses          1      0       -1     
+ Partials        1      0       -1

Impacted Files	Coverage Δ
src/index.js

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[vinhlh]

ping @evenchange4

[evenchange4]

Thanks!