Fixed handlebar spam messages from code coverage report generation

[nephix]

When running

$ cd raiden-dapp
$ npm run test:unit

we encounter the same spam messages from handlebars like in:

• Lots of handlebars warnings with text+coverage reporter jestjs/jest#9396
• Coverage in HTML view is broken jestjs/jest#9388 (comment)

To fix it, I had to remove node_modules and package-lock.json and run npm i again.

The new package-lock.json seems to have pinned a newer version of istanbul-reports that has a fix for this issue.

[kelsos]

lgtm thanks

[codecov]

Codecov Report

Merging #980 into master will not change coverage by %.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #980   +/-   ##
=======================================
  Coverage   96.24%   96.24%           
=======================================
  Files          93       93           
  Lines        3599     3599           
  Branches      728      728           
=======================================
  Hits         3464     3464           
  Misses         79       79           
  Partials       56       56           

Flag	Coverage Δ
#dapp	92.35% <ø> (ø)	⬆️
#sdk	97.93% <ø> (ø)	⬆️

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