Rename md-fab to mdFab

[robindijkhof]

Bug, feature request, or proposal:

Bug

What is the expected behavior?

From the beta.10 changelog:

All dash-case @directive selectors are deprecated in favor of the camelCase equivalent. The
dash-case selectors will be removed in a subsequent release. Some examples include:

What is the current behavior?

There is no mdFab

What is the use-case or motivation for changing an existing behavior?

Follow the standard

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

beta.10

[willshowell]

See #6720

[jelbourn]

See explanation in #6720

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