Update shaders_mesh_instancing.c

Due to this missing line of code the example seems is not going to work:
shader.locs[SHADER_LOC_MATRIX_MODEL] = GetShaderLocationAttrib(shader, "instanceTransform");

examples/shaders/shaders_mesh_instancing.c

@@ -73,6 +73,7 @@ int main(void)
     Shader shader = LoadShader(TextFormat("resources/shaders/glsl%i/lighting_instancing.vs", GLSL_VERSION),
                                TextFormat("resources/shaders/glsl%i/lighting.fs", GLSL_VERSION));
     // Get shader locations
+    shader.locs[SHADER_LOC_MATRIX_MODEL] = GetShaderLocationAttrib(shader, "instanceTransform");
     shader.locs[SHADER_LOC_MATRIX_MVP] = GetShaderLocation(shader, "mvp");
     shader.locs[SHADER_LOC_VECTOR_VIEW] = GetShaderLocation(shader, "viewPos");