Support jupyter-server-proxy >= 1.4.0

By default in 1.4.0, jupyter-server-proxy opens new
applications in an iframe. I don't think this should be the
default for most applications
(https://github.com/jupyterhub/jupyter-server-proxy/pull/198),
but regardless it is very nice to be explicit

jupyter_desktop/__init__.py

@@ -35,4 +35,5 @@ def setup_desktop():
         'port': 5901,
         'timeout': 30,
         'mappath': {'/': '/vnc_lite.html'},
+        'new_browser_window': True
     }

setup.py

@@ -10,7 +10,7 @@ setup(
             'desktop = jupyter_desktop:setup_desktop',
         ]
     },
-    install_requires=['jupyter-server-proxy>=1.2.0'],
+    install_requires=['jupyter-server-proxy>=1.4.0'],
     include_package_data=True,
     zip_safe=False
 )