Fix invalid json.

Should not have trailing space.

docs/source/development/wrapperkernels.rst

@@ -105,7 +105,7 b' Example'
 Here's the Kernel spec ``kernel.json`` file for this::
 
     {"argv":["python","-m","echokernel", "-f", "{connection_file}"],
-     "display_name":"Echo",
+     "display_name":"Echo"
     }