docs(tutorial): match html from angular-phonecat in step 7 instructions

Place phoneId binding in a proper HTML node

The code where the phoneId binding in the phone-detail.html template is first explained in step 7
of the tutorial doesn't make it a child of a proper HTML node, which makes the end-to-end test
against the view (also introduced in step 7) fail.

The test acquires the binding right from the view (by.binding('phoneId')), and apparently this
operation fails when the binding is not a child of an HTML node, and therefore the entire test also
fails. As soon as the binding is placed inside a <span></span> tag pair, the binding is found and
the test passes. The code on github for step 7 has it right, the binding is within the span tags,
but in the documentation I'm patching here the span's are missing.

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