* upgrade yargs and async dependencies.
were breaking change, but no impact according the tests
* upgrade yargs and package-lock.json
* add node 8 to the tested versions
* add node 8 to the allowed failures as requested
* add node 9 to travis build as acceptable failure and remove node 7
* Added nconf.any method
Fixes#126
Implemented on the Provider class
Takes an array of keys, or a variable argument list
Supports both callback and non-callback invocations
* Use an explicit search base in file store test
Fixes#224
Test file was created under process.env.HOME, but test was searching in
the current working directory. If the cwd was not on the same drive as
the home directory, the test would fail.
* Added some API documentation to README for 'any'
* Tweak `.any` documentation
