Fix feature|refactor|bug testing argument for string lenght

https://github.com/visionmedia/git-extras/commit/93d92ae3383b637d8b9ffd028bfdd15ae21d0591#diff-dde525a12e9f5e19

Seems only works while $2 is quoted, e.g. "$2"

Closes #241
Merge pull request #242 from sanusart/fix_feature_refactor_bug

Fix feature|refactor|bug testing argument for string length.