Merge pull request #10558 from takluyver/read-nb-utf8

Let nbformat take care of opening the file

IPython/core/interactiveshell.py

@@ -2506,8 +2506,7 b' class InteractiveShell(SingletonConfigurable):'
             """generator for sequence of code blocks to run"""
             if fname.endswith('.ipynb'):
                 from nbformat import read
-                with io_open(fname) as f:
-                    nb = read(f, as_version=4)
+                nb = read(fname, as_version=4)
                     if not nb.cells:
                         return
                     for cell in nb.cells: