ignore divide error in streamline (#1213)

* ignore divide error in streamline

* revert np error to original after division

Author: Kully

Diff for: plotly/figure_factory/_streamline.py

@@ -354,7 +354,11 @@ def get_streamline_arrows(self):
         dif_x = arrow_end_x - arrow_start_x
         dif_y = arrow_end_y - arrow_start_y
 
+        orig_err = np.geterr()
+        np.seterr(divide='ignore', invalid='ignore')
         streamline_ang = np.arctan(dif_y / dif_x)
+        np.seterr(**orig_err)
+
 
         ang1 = streamline_ang + (self.angle)
         ang2 = streamline_ang - (self.angle)