Merge pull request #49 from twrightsman/master

Update command-line flags for labextension enable

README.md

@@ -31,7 +31,7 @@ jupyter nbextension enable --py igv
 
 # If using a virtual environment
 jupyter serverextension enable --py igv --sys-prefix
-jupyter labextension enable igv --sys-prefix
+jupyter labextension enable igv --level sys_prefix
 jupyter nbextension install --py igv --sys-prefix
 jupyter nbextension enable --py igv --sys-prefix