waitForDocumentLoaded() throws an error

[johnringler]

I was really interested in using this custom command waitForDocumentLoaded() to speed up my tests.
However, it throws an error:

Error while running "execute" command: _this2.client.assertion is not a function
       TypeError: Error while running "execute" command: _this2.client.assertion is not a function
 at /project_path/node_modules/nightwatch-custom-commands-assertions/js/commands/waitForDocumentLoaded.js:76:31
           at NightwatchAPI.<anonymous> (/project_path/node_modules/nightwatch-custom-commands-assertions/js/commands/waitForDocumentLoaded.js:90:28)
           at Function.makePromise (/project_path/node_modules/nightwatch/lib/utils/index.js:128:28)
           at method.then (/project_path/node_modules/nightwatch/lib/index.js:130:62)
           at process._tickCallback (internal/process/next_tick.js:68:7)

If I just the waitForDocumentLoaded test from your module (nom run test), I also get the same error.

[pac-nvalenzuela]

I updated _this2.client.assertion to _this2.api.assert.ok