fix up a bunch of pytest.raises calls.

pizzathief · pizzathief · commit cd961ccad1a0 · 2016-01-22T00:05:19.000+11:00
I changed func,x,y into func(x,y) by mistake,
and hadn't changed a few back.
diff --git a/lib/matplotlib/tests/test_mlab.py b/lib/matplotlib/tests/test_mlab.py
@@ -1623,7 +1623,7 @@ def test_psd_detrend_mean_str_offset(self):
         assert_allclose(spec_g, spec_c, atol=1e-08)
         # these should not be almost equal
         pytest.raises(AssertionError,
-                      assert_allclose(spec_b, spec_c, atol=1e-08))
+                      assert_allclose, spec_b, spec_c, atol=1e-08)
 
     def test_psd_detrend_linear_func_trend(self):
         if self.NFFT_density is None:
