Fix 'display_shortcuts' with colors for grep -- close #4

There is a trailing color ESC char at the end of first filepath when you use
grep with colors. Actually, this is the colons after the filepatch which is
colorized.

When sack printing {grep,ack,ag} results with the related
[index], the end of that line is replace by the ESC char which means 'reset
all after that'.