Make possible to use size in percentage

[Strate]

Hello.
It is actually works (I can specify size in percentage for react-native-svg component), but emits warning. This PR removes that warning and allows to specify icon size in percentage

[robmadole]

@Strate can you speak more about why you needed percentage? This has me scratching my head a bit. I'm not against percentage but I'd like to understand it first.

[sam3d]

@robmadole I would also really benefit from this!

For example, I have a grid of icons that scale with the device size (i.e. each icon is 1/4 of the device width) and ideally being able to set the icons to automatically adopt that width instead of being limited to a specific number would make that much easier to accomplish.

This is likely fairly common with mobile devices, where many slightly different screen sizes could affect this functionality