Use GLSL 3.30 shaders

We currently ask for anything above 3.2 GL contexts, but we're still
using GLSL 1.50 shaders all over the place. If a GL driver supports GL
3.2+ and GLSL 1.50 only then we'd be in trouble, but the chances of that
happening are really small.

gdk/resources/glsl/gl3-texture-2d.fs.glsl

@@ -1,4 +1,4 @@
-#version 150
+#version 330
 
 in vec2 vUv;
 
@@ -7,5 +7,5 @@ out vec4 vertexColor;
 uniform sampler2D map;
 
 void main() {
-  vertexColor = texture2D (map, vUv);
+  vertexColor = texture (map, vUv);
 }

gdk/resources/glsl/gl3-texture-2d.vs.glsl

@@ -1,4 +1,4 @@
-#version 150
+#version 330
 
 in vec2 position;
 in vec2 uv;