Fixed bug #97

## Cause of bug

`__dir__.gsub(/\/lib(.?)+/, '')` is wrong regexp.
Therefore error occur when \_\_dir\_\_ contains 'lib' twice.

```
dir = '/Users/alpaca-tc/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/bundler/gems/watson-ruby-34a011943c7d/lib/watson'

p dir.gsub(/\/lib(.?)+/, '') + "/" + "assets/defaultConf" 
# got => "/Users/alpaca-tc/.rbenv/versions/2.0.0-p247/assets/defaultConf"
# expected => "/Users/alpaca-tc/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/bundler/gems/watson-ruby-34a011943c7d/assets/defaultConf"
```