Fix grammar and spacing in a warning message

IPython/core/magics/extension.py

@@ -43,8 +43,8 b' class ExtensionMagics(Magics):'
           -n filename : Specify a name for the file, rather than taking it from
                         the URL.
         """
-        warn("%install_ext` is deprecated, please distribute your extension(s)"
-             "as a python packages.", UserWarning)
+        warn("%install_ext` is deprecated, please distribute your extension "
+             "as a python package.", UserWarning)
         opts, args = self.parse_options(parameter_s, 'n:')
         try:
             filename = self.shell.extension_manager.install_extension(args,