fix a typo

Shaders/landmass.frag

@@ -69,7 +69,7 @@ void main (void)
 		float a = dot(VNormal, -V);
 		vec2 s = vec2(dot(V, VTangent), dot(V, VBinormal));
 
-                // prevent a device by zero
+                // prevent a divide by zero
                 if (a > -1e-3 && a < 1e-3) a = 1e3;
 		s *= depth_factor / a;
 		ds = s;