Coerced width and height config values to int

[summerisgone]

I've spent a day figuring out why tooltip isn't showing.
In c3_chart_internal_fn.tooltipPosition I got

chartRight = svgLeft + $$.currentWidth - $$.getCurrentPaddingRight();

with following values:

svgLeft = 0.5
$$.currentWidth = "800"

so I got chartRight around "0.5800".
The problem that I set width from HTML attribute as string. I think it worth nothing to cast them to int, it could saves anyone's time.

[codecov-io]

Current coverage is 64.05%

Merging #1713 into master will not change coverage

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