add cubic interpolation type

src/logic/scripting/lua/usertypes/lua_type_heightmap.cpp

@@ -229,8 +229,10 @@ static int l_resize(lua::State* L) {
         uint height = touinteger(L, 3);
         auto interpName = tostring(L, 4);
         auto interpolation = InterpolationType::NEAREST;
-        if (!std::strcmp(interpName, "linear")) {
+        if (std::strcmp(interpName, "linear") == 0) {
             interpolation = InterpolationType::LINEAR;
+        } else if (std::strcmp(interpName, "cubic") == 0) {
+            interpolation = InterpolationType::CUBIC;
         }
         heightmap->getHeightmap()->resize(width, height, interpolation);
     }