docs(page-objects.md): Refactor the existing Page Object example

[timothystone]

As presented, simply following the example will not run. This presents the Page Object example as a runnable set of spec + Page Object. See #4570

Open possibilities for future work include: carry the initial introduction over into a Page Object. Introduce world, etc.

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Thanks for your pull request. It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

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[timothystone]

I signed it

[googlebot]

CLAs look good, thanks!

[googlebot]

CLAs look good, thanks!

[timothystone]

How do you restart a build? looks like a timeout. Are there "tests" needed for this content?

[timothystone]

The travis error looks false, a process timeout. Can someone evaluate?

[qiyigg]

tests have been rerun and passed.