fix 'K' key binding

[mmckegg]

As per f/atom-term2#178, pressing 'K' just throws an error.

This PR fixes the bug!

[itsdarrylnorris]

To apply this patch locally on a Mac here are the steps:

cd ~/.atom/packages/term2/node_modules
rm -rf atom-term.js
git clone https://github.com/mmckegg/atom-term.js.git atom-term.js
cd atom-term.js
git checkout patch-1

[reqshark]

great PR! fixes OSX for me ⛵

@f please merge

[KylePDavis]

+1 fixes https://github.com/f/atom-term2/issues/178