Fix Dockerfile

Dockerfile

@@ -3,11 +3,14 @@ FROM alpine:3.13.0
 LABEL maintainer="Tomoya Tanjo <ttanjo@gmail.com>"
 
 ARG medal_ver=v0.4.0
+ARG medal_hook_ver=v0.0.2
 
 RUN apk --no-cache add ruby ruby-json ruby-etc nodejs jq docker-cli \
                        ruby-irb ruby-webrick bash curl && \
     curl -SL https://github.com/tom-tan/medal/releases/download/${medal_ver}/medal-linux-x86_64.tar.gz \
         | tar xC /usr/bin && \
+    curl -SL https://github.com/tom-tan/medal-hook/releases/download/${medal_hook_ver}/medal-hook-linux-x86_64.tar.gz \
+        | tar xC /usr/bin && \
     apk del --purge curl
 
 COPY . /ep3