colornames: update SVG 1.1 spec URL
colornames: update SVG 1.1 spec URL

The Scalable Vector Graphics (SVG) 1.1 specification URL has changed.
The old URL, https://www.w3.org/TR/SVG/, now hosts the SVG 2 spec.
SVG 1.1 spec has moved to https://www.w3.org/TR/SVG11/.

This change makes this package go generate successfully with no diff.

Change-Id: Ifa788b1bb47748610b3adc0ac96692c00bcb3158
Reviewed-on: https://go-review.googlesource.com/c/148566
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/image