Fix code comment

Author: leandrolcampos

tensorflow_probability/python/math/special_test.py

@@ -481,7 +481,7 @@ def betainc_partials_of_partial_x(a, b, x):
         betainc_partials_of_partial_b,
         betainc_partials_of_partial_x]
 
-    # Wrap in tf.function for faster computations.
+    # Wrap in tf.function and compile for faster computations.
     betainc_partials_of_partials = [
       tf.function(partial_fn, autograph=False, jit_compile=True)
       for partial_fn in betainc_partials_of_partials]