Fix: Bower breaks with console exception when run on package directory

@gaurave 

Fixes #3790.
Looks like there are multiple cases

* When a user click on a `bower.json` file, anything defined there is updated
* If a user click on top level project directory, it will find `bower.json` in the sub directory and run it
* If a user click on any other sub directory, it tries to find a `bower.json` in the parent.

Case 2 and 3 should be consistent. Either we look in the children or we look in parents. for `bower.json`.

I think looking in children sounds more intuitive. If no `bower.json` is present in a clicked directory, either `bower update` should not be in context menu or it should fail.