Updates usage of `co` to async function in src/scintillator/index.spec.js

[511V41]

fixes #636

P.S. I'm glad to committing to Bemuse because I'm beatmania IIDX player in Japan :)

Changelog

Migrate part of the code from co to async functions

[ghost]

I think that we can ignore issues that is raised by codeclimate. It saying "Similar blocks of code found in 2 locations. Consider refactoring" but they are obvious no problem.

[codecov-io]

Codecov Report

Merging #652 into master will increase coverage by 0.07%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #652      +/-   ##
==========================================
+ Coverage   80.91%   80.99%   +0.07%     
==========================================
  Files         156      156              
  Lines        4757     4782      +25     
  Branches      184      184              
==========================================
+ Hits         3849     3873      +24     
- Misses        859      860       +1     
  Partials       49       49

Impacted Files	Coverage Δ
src/scintillator/index.spec.js	99.6% <100%> (-0.4%)	:arrow_down:

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[dtinth]

Closing as I just realized that this PR has already been cherry-picked into master — df0e85a918a261d0af15e50a01251c9e50cede88