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