Merge pull request #2343 from ian-r-rose/fix_unlink

Fix file path.

docs/extensions_dev.md

@@ -113,7 +113,7 @@ repository for an extension npm package. This operation may be subsequently
 reversed by running
 
 ```
-npm run addsibling <extension-name>
+npm run removesibling <extension-dir-name>
 ```
 
 This will remove the package metadata from the source tree, but wil **not**

jupyterlab/commands.py

@@ -229,7 +229,7 @@ def uninstall_extension(name, app_dir=None):
     if app_dir == here:
         raise ValueError('Cannot install packages in core app')
     # Allow for uninstalled core extensions here.
-    with open(pjoin(here, 'package.json')) as fid:
+    with open(pjoin(here, 'package.app.json')) as fid:
         data = json.load(fid)
         if name in data['jupyterlab']['extensions']:
             print('Uninstalling core extension %s' % name)