fix inconsistent graph problem

[ign-packo]

Motivation

En lien avec le ticket interne #2016. L'application de certaines corrections fait apparaître des lignes parasites dans le graphe de mosaiquage.

Principe

Ces problèmes sont connus dans le module pureimage que l'on utilise pour rasteriser les patchs (https://github.com/joshmarinacci/node-pureimage/issues/62). La solution proposée consiste à remplacer ce module (qui ne semble pas très actifs) par le module https://github.com/Automattic/node-canvas qui semble beaucoup plus actifs et beaucoup plus utilisés.

[coveralls]

Pull Request Test Coverage Report for Build 1424895787

• 7 of 7 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.03%) to 94.883%

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Totals
Change from base Build 1412749338:	0.03%
Covered Lines:	4982
Relevant Lines:	5232

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 1424828212

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 7 of 7 (100.0%) changed or added relevant lines in 2 files are covered.
• 11 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.04%) to 94.886%

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Files with Coverage Reduction	New Missed Lines	%
middlewares/patch.js	11	93.72%
<!--	Total:	11		-->

Totals
Change from base Build 1412749338:	0.04%
Covered Lines:	4985
Relevant Lines:	5235

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💛 - Coveralls