[fix] Disable numerical jvp checks for complex sign function.

tests/test_systematic.py

@@ -1,5 +1,5 @@
 from __future__ import absolute_import
-import numpy as onp
+mport numpy as onp
 import autograd.numpy.random as npr
 import autograd.numpy as np
 import operator as op
@@ -44,7 +44,7 @@ def test_log1p():   unary_ufunc_check(np.log1p, lims=[0.2, 2.0])
 def test_log2():    unary_ufunc_check(np.log2,  lims=[0.2, 2.0])
 def test_rad2deg(): unary_ufunc_check(lambda x : np.rad2deg(x)/50.0, test_complex=False)
 def test_radians(): unary_ufunc_check(np.radians, test_complex=False)
-def test_sign():    unary_ufunc_check(np.sign)
+def test_sign():    unary_ufunc_check(np.sign, test_complex=False)
 def test_sin():     unary_ufunc_check(np.sin)
 def test_sinh():    unary_ufunc_check(np.sinh)
 def test_sqrt():    unary_ufunc_check(np.sqrt, lims=[1.0, 3.0])