Spheres model matrix generation fix

Fix of integer division resulting in some spheres being rendered at same position.
Removed redundant float cast as all operands are being promoted to double anyways.

src/6.pbr/1.1.lighting/lighting.cpp

@@ -143,8 +143,8 @@ int main()
                 
                 model = glm::mat4();
                 model = glm::translate(model, glm::vec3(
-                    (float)(col - (nrColumns / 2)) * spacing, 
+                    (col - (nrColumns / 2.)) * spacing, 
-                    (float)(row - (nrRows / 2)) * spacing, 
+                    (row - (nrRows / 2.)) * spacing, 
                     0.0f
                 ));
                 shader.setMat4("model", model);