upgrade server and build-extension

buildutils/src/build-extension.ts

@@ -20,9 +20,8 @@ import { run } from './utils';
 
 commander
   .description('Build an extension')
-  .usage('[options] <path>')
   .option('--prod', 'build in prod mode (default is dev)')
-  .option('--core-path <path>', 'the core package directory')
+  .requiredOption('--core-path <path>', 'the core package directory')
   .option('--watch')
   .action(async cmd => {
     let node_env = 'development';

setup.py

@@ -151,7 +151,7 @@ setup_args = dict(
 setup_args['install_requires'] = [
     'ipython',
     'tornado!=6.0.0, !=6.0.1, !=6.0.2',
-    'jupyterlab_server>=2.0.0a2',
+    'jupyterlab_server>=2.0.0a3',
     'jupyter_server>=1.0.0rc5',
     'nbclassic>=0.2.0rc3',
     'jinja2>=2.10'