MXS-1300: Use single quotes in Node.js code

The Node.js code should use single quotes as it appears to be a prevalent
style choice for Node.js applications.

client/maxctrl/lib/show.js

@@ -83,9 +83,9 @@ exports.builder = function(yargs) {
                 {'Commands': 'attributes.commands'}
             ])
         })
-        .usage("Usage: show <command>")
+        .usage('Usage: show <command>')
         .help()
         .command('*', 'the default command', {}, () => {
-            console.log("Unknown command. See output of 'help show' for a list of commands.")
+            console.log('Unknown command. See output of `help show` for a list of commands.')
         })
 }