Fix actual canvas element not maintaining aspect ratio

[ning-y]

Resolves #241.

The canvas element was not maintaining its aspect ratio, but the visuals of the canvas element were. Resulted in the visuals and their hover areas being 'out of sync'. Fixed with the oldest css trick in the book.

[coveralls]

Pull Request Test Coverage Report for Build 479

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 25.405%

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Totals
Change from base Build 475:	0.0%
Covered Lines:	776
Relevant Lines:	2606

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💛 - Coveralls

[ning-y]

@remo5000 Let's settle #240 first because I wanna stage a new version with that PR and this PR (and the version bump is at this PR so this one has to go second).