Update zsh config

1. Plugin laravel5 not found in zsh plugin list.
2. The executable command for the composer package could not be found. For example 'laravel new xxx'. The zsh composer plugin solves this problem.

workspace/Dockerfile

@@ -1560,7 +1560,7 @@ ARG SHELL_OH_MY_ZSH_ALIASES=false
 USER laradock
 RUN if [ ${SHELL_OH_MY_ZSH} = true ]; then \
     sh -c "$(curl -fsSL https://raw.githubusercontent.com/ohmyzsh/ohmyzsh/master/tools/install.sh) --keep-zshrc" && \
-    sed -i -r 's/^plugins=\(.*?\)$/plugins=(laravel5)/' /home/laradock/.zshrc && \
+    sed -i -r 's/^plugins=\(.*?\)$/plugins=(laravel composer)/' /home/laradock/.zshrc && \
     echo '\n\
 bindkey "^[OB" down-line-or-search\n\
 bindkey "^[OC" forward-char\n\