Array.prototype.__au_patched__ should not be enumerable

[zakjan]

I'm submitting a bug report

• Library Version:
  1.7.2, 2.1.3

Please tell us about your environment:

• Node Version:
  9.11.1

• NPM Version:
  6.3.0

• JSPM OR Webpack AND Version
  webpack 4.16.4

• Browser:
  Chrome 68

• Language:
  TypeScript 2.9.2

Current behavior:
Array.prototype.__au_patched__ is enumerable, for (var i in array) iterates over it

Expected/desired behavior:

• What is the expected behavior?
  Array.prototype.__au_patched__ should not be enumerable

• What is the motivation / use case for changing the behavior?
  fix breaking change caused by fix(ArrayObservation): ensure patch applied only once #704

[bigopon]

@zakjan my rookie mistake. Thanks for this issue.

[zakjan]

Thanks for the fast fix!