Fix query line highlight

I fixed a tiny bug in https://github.com/peco/peco/pull/131.
Currently peco highlights the query word only when caretPos is in the end of query word.

## before
![](https://camo.githubusercontent.com/f7b7cf62d06501313a473d7844e02aa6324796a8/687474703a2f2f6769667a6f2e6e65742f61313557393056344b332e676966)

## after
![](http://gifzo.net/BTLxAfRkYTI.gif)