Bugfix for #10

[fixed problem with nested arrays](https://github.com/flitbit/diff/issues/10)
Merge pull request #1 from paulpflug/patch-1

Bugfix for #10
Changed check for required properties on `change`
requirement of instanceof Diff is way to strong
added function revertChange, which reverts a single `change` item
Revert "added function revertChange, which reverts a single `change` item"

This reverts commit 414007f0b6b8f797d6bfe7044fd0ca427232ad9e.
Revert "Bugfix for #10"

This reverts commit 2056c016a771d677cbae699fb7953bfeb8964be2.
Merge pull request #13 from paulpflug/checkForDiff

Changed check for required properties on `change`