title: Error occurred while running .getAttribute() command on <csselement>: TypeError: _this2.client.assertion is not a function
body: <p>While creating nightwatch tests, I used <code>waitForAttribute()</code> and it works with nightwatch@0.9.0. But when I tried to upgrade to the nightwatch@1.0.6, it gives following error:</p>
  
  <pre><code>An error occurred while running .getAttribute() command on &lt;.csselement&gt;: TypeError: _this2.client.assertion is not a function
    at /node_modules/nightwatch-custom-commands-assertions/js/commands/waitForAttribute.js:100:19
    at NightwatchAPI.&lt;anonymous&gt; (.../node_modules/nightwatch-custom-commands-assertions/js/commands/waitForAttribute.js:117:13)
    at transport.locateElement.then.then.result (../node_modules/nightwatch/lib/api-loader/element-command.js:107:23)
    at &lt;anonymous&gt;
    at process._tickCallback (internal/process/next_tick.js:188:7)
     at &lt;anonymous&gt;
     at process._tickCallback (internal/process/next_tick.js:188:7)
     at &lt;anonymous&gt;
     at process._tickCallback (internal/process/next_tick.js:188:7)
  </code></pre>