Fixed incorrect lengths for colorized strings in ASCII table

Related to: https://github.com/wp-cli/php-cli-tools/issues/59
Bug looks this way: 
![ascii-table-bug](https://cloud.githubusercontent.com/assets/1533818/4773555/3405a0cc-5ba4-11e4-9737-20a00e972c4d.gif)

I've added failing test for this case, but couldn't find the reason yet.
Will try to check later also.