Add #version 120 to make shaders work on Windows

USL-32

plugins/LayerView/layers.shader

@@ -1,5 +1,6 @@
 [shaders]
 vertex =
+    #version 120
     uniform highp mat4 u_modelViewProjectionMatrix;
     uniform lowp float u_active_extruder;
     uniform lowp float u_shade_factor;
@@ -28,6 +29,7 @@ vertex =
     }
 
 fragment =
+    #version 120
     varying lowp vec4 v_color;
     varying float v_line_type;