[Enhancement] Make Canvas Invocations of measureText Node Canvas Compliant

[jonobr1]

Is your feature request related to a problem? Please describe.
Two.js uses context.measureText from HTML5 <canvas /> tags to know what the width of a set of rendered text is in Two.Text.getBoundingClientRect.

This works in the browser, but not in headless environments

Describe the solution you'd like
node-canvas is the defacto Canvas feature for node.js and one recommended for use with Two.js on its own documentation page. So, the measureText code in Two.Text should work with node-canvas as well as the browser.

This issue is based on the conversation here: #668