Zsh completion: permit multiple --file arguments

Before this change:

```
$ docker-compose --file docker-compose.yml -<TAB>
 -- option --
--help                 -h  -- Get help
--host                 -H  -- Daemon socket to connect to
--project-name         -p  -- Specify an alternate project name (default: directory name)
--skip-hostname-check      -- Don't check the daemon's hostname against the name specified in the client certificate (for example if your docker host is an IP address)
--tls                      -- Use TLS; implied by --tlsverify
--tlscacert                -- Trust certs signed only by this CA
--tlscert                  -- Path to TLS certificate file
--tlskey                   -- Path to TLS key file
--tlsverify                -- Use TLS and verify the remote
--verbose                  -- Show more output
--version              -v  -- Print version and exit
```

(Note the `--file` argument is no longer available to complete.)

After this change:

```
docker-compose --file docker-compose.yml -<TAB>
 -- option --
--file                 -f  -- Specify an alternate docker-compose file (default: docker-compose.yml)
--help                 -h  -- Get help
--host                 -H  -- Daemon socket to connect to
--project-name         -p  -- Specify an alternate project name (default: directory name)
--skip-hostname-check      -- Don't check the daemon's hostname against the name specified in the client certificate (for example if your docker host is an IP address)
--tls                      -- Use TLS; implied by --tlsverify
--tlscacert                -- Trust certs signed only by this CA
--tlscert                  -- Path to TLS certificate file
--tlskey                   -- Path to TLS key file
--tlsverify                -- Use TLS and verify the remote
--verbose                  -- Show more output
--version              -v  -- Print version and exit
```

Signed-off-by: Matt Bray <[email protected]>

contrib/completion/zsh/_docker-compose

@@ -388,7 +388,7 @@ _docker-compose() {
 
     _arguments -C \
         '(- :)'{-h,--help}'[Get help]' \
-        '(-f --file)'{-f,--file}'[Specify an alternate docker-compose file (default: docker-compose.yml)]:file:_files -g "*.yml"' \
+        '*'{-f,--file}'[Specify an alternate docker-compose file (default: docker-compose.yml)]:file:_files -g "*.yml"' \
         '(-p --project-name)'{-p,--project-name}'[Specify an alternate project name (default: directory name)]:project name:' \
         '--verbose[Show more output]' \
         '(- :)'{-v,--version}'[Print version and exit]' \