Fixes #294: Tab completion repeats the first character (oh-my-zsh)

[aral]

Fixes #294

To test:

Using oh-my-zsh with the Extraterm setup injected into the session, (e.g., Agnoster theme; although theme is not a factor):

Before PR:

1. Open a terminal and carry out tab-completion on, say, the letter c
2. Notice that the c character is repeated.

After PR:

Notice that the c character is not repeated.

[sedwards2009]

From https://stackoverflow.com/questions/19305291/remnant-characters-when-tab-completing-with-zsh

""" You indicate that a character sequence in the zsh prompt has zero width using the %{ and %} delimiters. """

This is exactly the fix we need!

Thanks.

[aral]

Thanks :)