Update github.com/go-gl/gl commit hash to 726fda9

Author: renovate-bot

go.mod

@@ -10,7 +10,7 @@ require (
 	github.com/galaco/source-tools-common v0.1.0
 	github.com/galaco/tinygametools v0.1.0
 	github.com/galaco/vtf v1.2.0 // indirect
-	github.com/go-gl/gl v0.0.0-20190320180904-bf2b1f2f34d7
+	github.com/go-gl/gl 726fda9656d6
 	github.com/go-gl/mathgl v0.0.0-20190713194549-592312d8590a
 	github.com/galaco/filesystem v0.1.3
 	github.com/galaco/vmt v0.1.3 // indirect