Fix bad reference to census_shapes.yml using RVM.

[weshays]

...This commit fixes the error _No such file or directory - lib/yml/censusshapes.yml.

To repo the error:

• Start rails console
• Create an instance of CensusApis::Client
  client = CensusApi::Client.new(CENSUS_API_KEY)
• Run command client.sf1('P0010001', 'STATE:06')

You will get "Errno::ENOENT: No such file or directory - lib/yml/census_shapes.yml"

The issue was the path was was trying to look into the project lib directory instead of the gem.