build with electron 1.3.7

fixes #12570

Using Cmd+Scroll to zoom on a mac

Bgashler1/watermark tweeks

Fixed: Markdown syntax highlighting to support alternative header styles

This may have been a Chrome bug causing terminal-outer-container to be
positioned incorrectly when the terminal had focus. Instead of investigating
further just move to a simpler implementation without flexbox.

Fixes #12038

Fixes #12574