Fix "Error while reading file" Fish completion

An unbalanced single quote caused Fish to fail to load the completion file with `source: Error while reading file “/etc/fish/completions/docker.fish”`.

Docker-DCO-1.1-Signed-off-by: Andrew France <andrew@avito.co.uk> (github: Odaeus)
Merge pull request #6852 from Odaeus/patch-1

Fix "Error while reading file" in Fish completion
Fix the parent/child relationship in the docs

In the Docker Linking Docs, the parent child relationship
was backwards. The Web container should be able to access
the DB, not other way around. Furthermore, the output of
'docker ps' was wrong (it showed that the DB could access
the Web). This fixes both typos.

Docker-DCO-1.1-Signed-off-by: Ian Bull <irbull@gmail.com> (github: irbull)