number min/max/greater/less do not allow decimal values

[Justin-Kuehn]

This:

var Joi = require('joi');
Joi.number().min(0.1).required()

Throws:

Error: limit must be an integer
    at Object.exports.assert (.\node_modules\joi\node_modules\hoek\lib\index.js:678:11)
    at internals.Number.greater (.\node_modules\joi\lib\number.js:83:10)
    at Object.<anonymous> (.\test.js:6:27)
    at Module._compile (module.js:449:26)
    at Object.Module._extensions..js (module.js:467:10)
    at Module.load (module.js:349:32)
    at Function.Module._load (module.js:305:12)
    at Function.Module.runMain (module.js:490:10)
    at startup (node.js:124:16)
    at node.js:807:3

The same happens with max, greater, and less.

[Justin-Kuehn]

I made a pull request here: #610

Thanks!