Add zsh completion for 'docker-compose build --build'

Signed-off-by: Steve Durrheimer <s.durrheimer@gmail.com>

contrib/completion/zsh/_docker-compose

@@ -193,6 +193,7 @@ __docker-compose_subcommand() {
             _arguments \
                 $opts_help \
                 '--no-cache[Do not use cache when building the image]' \
+                '--pull[Always attempt to pull a newer version of the image.]' \
                 '*:services:__docker-compose_services_from_build' && ret=0
             ;;
         (help)