Replace lowercase {@inheritdoc} with @inheritDoc

Replace lowercase {@inheritdoc} with @inheritDoc

According to the coding standards we even enforce with a custom PHPCS sniff.
It currently does not pick these mistakes up because of the curly brackets.
I'm not sure if this is worth an update of the PHPCS sniff. I wanted to
suggest this fix anyway.

Change-Id: I9041ea7a00baf7f55e0ff0e56879a89fb74bb479