Mark display as no coverage

(should eventually figure out how to mock/cover this)

Author: Martin Durant

streamz/core.py

@@ -333,7 +333,7 @@ def __str__(self):
 
     __repr__ = __str__
 
-    def _ipython_display_(self, **kwargs):
+    def _ipython_display_(self, **kwargs):  # pragma no cover
         try:
             from ipywidgets import Output
             from IPython.core.interactiveshell import InteractiveShell