Properly document :raising_hand:

The emoji cheat sheet used to say that you could type in `:raised_hand:`
to get a woman raising her hand. However, actually doing so on GitHub
and other sites just gives you a :hand:

You can see that here:
hand: :hand:
raised_hand: :raised_hand:
raising_hand: :raising_hand:

To get the desired emoji, you actually need to type `:raising_hand:`

This updates the images and HTML appropriately to reflect that change.