fix undefined Canvg reference

[antonkri97]

If we will unignore svg.spec.js test file we will get the following error:

TypeError: Cannot read property 'fromString' of undefined
    at <Jasmine>
    at src/modules/svg.js:135:30
    at async UserContext.<anonymous> (test/specs/svg.spec.js:19:5)

After my fix at least we will have access to the required fromString api, but the test will continue to fail due to the incompatibility of different browsers, as indicated in the svg.spec.js source code.

[HackbrettXXX]

Alright, thanks for the PR :)