Skip prototype properties

To be a proper object-keys shim, it has to only iterate over own properties.

Would you be OK adding a dependency, `object-keys`? It's a well-tested Object.keys shim.
Merge pull request #76 from ljharb/patch-1

Skip prototype properties
Merge pull request #81 from sebs/master

Cleanup of the Tests
use blacklist instead of nullary objects
Merge pull request #86 from eivindfjeldstad/master

use blacklist instead of nullary objects
Release 0.6.6
Make `make test` work on Windows.

Quoting the filename avoids the following error on Windows:

> '.' is not recognized as an internal or external command,
> operable
program or batch file.
> make: *** [test] Error 1
Merge pull request #87 from davidmurdoch/patch-1

Make `make test` work on Windows.