Fix write stream error

[vnenkpet]

I've been running into a problem where in about 1 of 150 requests failed with uncaught ENOENT exception.

Following suggestion from this http://stackoverflow.com/questions/12906694/fs-createwritestream-does-not-immediately-create-file I tried adding a piece of code and now it seems that the code is alwyas handled properly... I tried running 1000 tests several times and no problem occured.

However note I am not 100% sure it actually solved this and that it was not just a lucky coincidence.

I've also made some adjustments to the code that ESLint and IDE were complaining about (missing semicolons, wrong JSDoc parameters etc, let where const was more appropriate etc)

[codecov-io]

Codecov Report

Merging #12 into master will increase coverage by 0.21%.

@@            Coverage Diff             @@
##           master      #12      +/-   ##
==========================================
+ Coverage    93.9%   94.11%   +0.21%     
==========================================
  Files           1        1              
  Lines          82       85       +3     
  Branches        5        6       +1     
==========================================
+ Hits           77       80       +3     
  Misses          5        5

Impacted Files	Coverage Δ
index.js	94.11% <91.11%> (+0.21%)	:white_check_mark:

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[christensson]

@vnenkpet Did this solve the issue?

As stated in a comment in the first reply to http://stackoverflow.com/questions/12906694/fs-createwritestream-does-not-immediately-create-file the WritableStream returned from fs.createWriteStream already waits for the "open" event before writing to the file.

[vnenkpet]

@christensson It did solve the issue. We didn't have any problems with this since then... Thanks for merging!