Update doc/de/intro/index.md

German Intro
Passing the wrong object to hasOwnProperty method.
Cosmetic.
Update undefined.md

Delete the duplicate text.
correct the translation of  number in equality.md
Merge pull request #168 from huanglong/master

correct the translation of number in equality.md
Merge pull request #167 from Luzi/patch-1

Update undefined.md
Merge pull request #158 from PiNotEqual3/patch-1

Update doc/de/intro/index.md
Merge pull request #159 from brunocoelho/dev

Passing wrong object to hasOwnProperty method.