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

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

contrib/completion/zsh/_docker-compose

@@ -329,6 +329,7 @@ __docker-compose_subcommand() {
             _arguments \
                 $opts_help \
                 '(--abort-on-container-exit)-d[Detached mode: Run containers in the background, print new container names.]' \
+                '--build[Build images before starting containers.]' \
                 '--no-color[Produce monochrome output.]' \
                 "--no-deps[Don't start linked services.]" \
                 "--force-recreate[Recreate containers even if their configuration and image haven't changed. Incompatible with --no-recreate.]" \