unicode literals in notebook magic tests

per review by @takluyver

IPython/core/tests/test_magic.py

@@ -420,13 +420,13 b' def test_extension():'
 def test_notebook_export_json():
     with TemporaryDirectory() as td:
         outfile = os.path.join(td, "nb.ipynb")
-        _ip.ex(py3compat.u_format("u = {u}'héllo'"))
+        _ip.ex(py3compat.u_format(u"u = {u}'héllo'"))
         _ip.magic("notebook -e %s" % outfile)
 
 def test_notebook_export_py():
     with TemporaryDirectory() as td:
         outfile = os.path.join(td, "nb.py")
-        _ip.ex(py3compat.u_format("u = {u}'héllo'"))
+        _ip.ex(py3compat.u_format(u"u = {u}'héllo'"))
         _ip.magic("notebook -e %s" % outfile)
 
 def test_notebook_reformat_py():
@@ -435,7 +435,7 b' def test_notebook_reformat_py():'
         with io.open(infile, 'w') as f:
             current.write(nb0, f, 'json')
             
-        _ip.ex(py3compat.u_format("u = {u}'héllo'"))
+        _ip.ex(py3compat.u_format(u"u = {u}'héllo'"))
         _ip.magic("notebook -f py %s" % infile)
 
 def test_notebook_reformat_json():
@@ -444,7 +444,7 b' def test_notebook_reformat_json():'
         with io.open(infile, 'w') as f:
             current.write(nb0, f, 'py')
             
-        _ip.ex(py3compat.u_format("u = {u}'héllo'"))
+        _ip.ex(py3compat.u_format(u"u = {u}'héllo'"))
         _ip.magic("notebook -f ipynb %s" % infile)
         _ip.magic("notebook -f json %s" % infile)