Return early on non-Joi errors

[randyxli]

Hapi allows defining custom validation functions in the validate route option (see the test in the PR). These functions can throw an error that's not a Joi error, which triggers a type error in Relish:

Debug: internal, implementation, error 
    TypeError: Cannot read property 'map' of undefined
    at Relish.parseError (/Users/randy/src/relish/index.js:17:106)
    at Relish.exports.failAction (/Users/randy/src/relish/index.js:61:105)
    at module.exports.internals.Manager.execute (/Users/randy/src/relish/node_modules/hapi/lib/toolkit.js:35:57)
    at module.exports.internals.Manager.failAction (/Users/randy/src/relish/node_modules/hapi/lib/toolkit.js:99:21)
    at Object.internals.input (/Users/randy/src/relish/node_modules/hapi/lib/validation.js:120:34)
    at process._tickCallback (internal/process/next_tick.js:68:7)

Since Relish is designed to handle Joi errors, this PR proposes to fix the error by early returning when the handled error is not a Joi error.

Separately, to test I installed Boom, which caused huge changes in the package-lock.json. If you have any tips on how to minimize those changes, I'm all ears. Thanks for considering my PR!

[coveralls]

Coverage remained the same at 100.0% when pulling 16a88cc on randyxli:custom-validation into 9d570fa on dialexa:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 16a88cc on randyxli:custom-validation into 9d570fa on dialexa:master.