getActionClient broken in 2.2.0

[chfritz]

See https://github.com/RethinkRobotics-opensource/rosnodejs/pull/65/files#r173348798.

To reproduce, just run the example shown in the code:

      let ac = rosNode.getActionClient({
        type: "turtle_actionlib/ShapeAction",
        actionServer: "/turtle_shape"
      });

Which will result in an error like this:

/home/cfritz/work/rosjs/src/lib/NodeHandle.js:210
      throw new Error(`Unable to create action client ${actionServer} without type - got ${type}`);
      ^

Error: Unable to create action client [object Object] without type - got undefined
    at NodeHandle.actionClientInterface (/home/cfritz/work/rosjs/src/lib/NodeHandle.js:210:13)
    at Object.getActionClient (/home/cfritz/work/rosjs/src/index.js:334:20)
    at Timeout._onTimeout (/home/cfritz/work/rosjs/src/examples/turtle.js:82:26)
    at ontimeout (timers.js:475:11)
    at tryOnTimeout (timers.js:310:5)
    at Timer.listOnTimeout (timers.js:270:5)

It's easy to fix. I'll create a PR.