fix: Add support of browsers not supporting unicode regexp

[pavel-krasnov]

Hi, when running the package in old browsers (Chrome < 50) I get the error "Invalid flags supplied to RegExp constructor 'u'". This is because of this line of code:

const dataURI = /^data:image\/svg[^,]*?(;base64)?,(.*)/u.exec(src);

This feature (/u) is supported from Chrome 50: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/unicode#browser_compatibility

Why could somebody need to support Chrome 50? I am developing a WebOS/Tizen web based app. Some not so old TV devices use these old Chrome versions under the hood to run apps:

• WebOS 3: https://webostv.developer.lge.com/develop/specifications/web-api-and-web-engine
• Tizen 3: https://developer.samsung.com/smarttv/develop/specifications/web-engine-specifications.html

As the main page of this repo effectively mentions support for Chrome 42+ (from which fetch is supported) or even older with fetch polyfill, it would be great to change the line to something processable in old browsers.

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