Use ES5 `Object.keys` instead of Underscore.js `keys`
Use ES5 `Array.isArray` instead of Underscore.js `isArray`
Use ES5 `obj.some` and `obj.every` instead of Underscore.js `any` and `all`
Revert "Use ES5 `obj.some` and `obj.every` instead of Underscore.js `any` and `all`"

This reverts commit f4f620e0c11a973be9295db887f5f0aa7cee9f64.
Merge pull request #406 from watson/es5

Use ES5 native instead of Underscore.js when possible