Update documentation of `hGetContents` and `hGetContentsN`.

[danidiaz]

The documentation states the following about hGetContents and hGetContentsN:

The handle is closed on EOF.

Looking at the code, that doesn't seem to be the case. And that is good! It makes more sense this way and fits better with how pipes-bytestring works. So perhaps the documentation should be updated, removing the references to handles being closed on EOF.

[fosskers]

Fixed. Sorry this took so long to do.