Update .github/action/Dockerfile

Author: ericbn

.github/action/Dockerfile

@@ -1,6 +1,4 @@
 FROM alpine:latest
 RUN apk add -U --no-cache zsh coreutils curl expect git ncurses perl gnuplot
-# Change default shell from ash to zsh
-RUN sed -i -e "s/bin\/ash/bin\/zsh/" /etc/passwd
 ENV TERM=xterm-256color
 ENTRYPOINT ["zsh", "-c"]