Replace deprecated canvas-prebuilt by canvas

[michalochman]

Fixes #94

@matthieu-foucault also added the cross-env dev dependency, allowing to run build scripts on windows

[michalochman]

@matthieu-foucault looks like tests do not pass when you remove canvas-prebuilt from dependencies.

TypeError: Cannot set property 'fillStyle' of null

[michalochman]

Looks like this is because the current jest version is using jsdom that can not work with canvas@2 yet.

https://github.com/facebook/jest/blob/d792940b01ee1e17e435574e6cf4830b5186245e/packages/jest-environment-jsdom/package.json#L14

[matthieu-foucault]

The tests for this PR did pass on CircleCI though 🤔

[michalochman]

That's because canvas-prebuilt is still in devDependencies ;)

I have solution to it thought through custom jest environment thought so I'll update this PR shortly.

[matthieu-foucault]

That's because canvas-prebuilt is still in devDependencies ;)

🤦‍♂️

[codecov]

Codecov Report

Merging #97 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #97   +/-   ##
=======================================
  Coverage   95.67%   95.67%           
=======================================
  Files          11       11           
  Lines         231      231           
=======================================
  Hits          221      221           
  Misses         10       10

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