fix example code in "registering procedures" of "programming" doc (#541)
fix example code in "registering procedures" of "programming" doc (#541)

As far as I can tell, the existing version there was not syntactically valid javascript.
crossbario/autobahn-js,tavendo/AutobahnJS,crossbario/autobahn-js,crossbario/autobahn-js,tavendo/AutobahnJS,tavendo/AutobahnJS,crossbario/autobahn-js