Fixes indentation

Before this commit, `lib/cron.js` was a hodge podge
of tab indentation and two-space indentation.

This commit changes all tab indents to two spaces.

It might be noted that for the first three lines (2-4), I left the indentation at 4 spaces (well, from 2 tabs) - if this is not well received (ahh! no!) it can be changed back to two spaces.