Modified during iteration in upgrade extension

[agoose77]

jupyterlab/jupyterlab/upgrade_extension.py

Lines 83 to 86 in 0b46ba0

	for (key, value) in data[name].items():
	if key.startswith('@phosphor/'):
	has_phosphor = True
	data[name][key.replace('@phosphor/', '@lumino/')] = value

We should take a copy of the items view to prevent this
for (key, value) in list(data[name].items())