Fix setting of default values

[mykola-mokhnach]

Object.assign is sometimes not exactly we'd like to use for setting the default values. For example:

d = _.defaults({a: 1}, {b:2}, {c:undefined, a:undefined});
JSON.stringify(d) //{ "a":1,"b":2}

d = Object.assign({a: 1}, {b:2}, {c:undefined, a:undefined});
JSON.stringify(d) //{ "a":1undefined, "b":2, "c": undefined}

Addresses appium/appium#12409

[dpgraham]

Looks good. I wish there was a lint rule that could catch this type of problem.

[imurchie]

You can also just flip the Object.assign arguments:

> d = _.defaults({a: 1}, {b:2}, {c:undefined, a:undefined});
{ a: 1, b: 2, c: undefined }
> d = Object.assign({a: 1}, {b:2}, {c:undefined, a:undefined});
{ a: undefined, b: 2, c: undefined }
> JSON.stringify(d) //{ "a":1undefined, "b":2, "c": undefined}
'{"b":2}'
> d = Object.assign({c:undefined, a:undefined}, {a: 1}, {b:2});
{ c: undefined, a: 1, b: 2 }