Fix "'module' object has no attribute 'display'" for old ipython.

Author: theengineear

Diff for: plotly/tools.py

@@ -33,6 +33,7 @@ def warning_on_one_line(message, category, filename, lineno, file=None, line=Non
 
 try:
     import IPython
+    import IPython.core.display
     _ipython_imported = True
 except ImportError:
     _ipython_imported = False