Fix colors deprecated message

[gabrielokura]

Using version 2.0.5 of the package.

This is the warning message direct from flutters framework. It isn't suggesting the use of colorFilter instead of color.

It should be like the documentation from pub.dev (last item of deprecations)

Also, fix the documentation of SvgPicture.asset which is implying the use of deprecated members.

// The color and colorBlendMode arguments, if specified, will be used to set a [ColorFilter] on any [Paint]s created for this drawing.

[PhiFry]

But why did they even remove color and colorBlendMode, its just more annoying to specify a custom colorFilter.