progs/glsl: Fix memory leak in deriv.c.
diff --git a/progs/glsl/deriv.c b/progs/glsl/deriv.c
index 265a515..30f2b75 100644
--- a/progs/glsl/deriv.c
+++ b/progs/glsl/deriv.c
@@ -140,6 +140,7 @@
    glNewList(SphereList, GL_COMPILE);
    gluSphere(obj, 2.0f, 30, 15);
    glEndList();
+   gluDeleteQuadric(obj);
 }