add space in the welcome message (#561)

Author: echarles

jupyter_server/serverapp.py

@@ -2329,7 +2329,7 @@ def start_app(self):
             info(_i18n("Welcome to Project Jupyter! Explore the various tools available"
                  " and their corresponding documentation. If you are interested"
                  " in contributing to the platform, please visit the community"
-                 "resources section at https://jupyter.org/community.html."))
+                 " resources section at https://jupyter.org/community.html."))
 
         self.write_server_info_file()
         self.write_browser_open_files()