Fix incompatibility with npm 3

[Andrew Goode]

yargonaut is expecting y18n to be installed under yargs from the parent module (i.e. expecting nested node_modules), but npm 3 installs modules in a flattened structure, causing yargonaut to be ineffective (i.e. gracefully and silently skipped).

Need to tweak the logic that finds and intercepts y18n to account for installed module structure with npm 3 as well as npm 2.