Update Dockerfile

Author: lmc999

Dockerfile

@@ -5,5 +5,6 @@ COPY check.sh /check.sh
 RUN chmod +x /check.sh && \
     apk add --no-cache curl wget bash && \
     apk add  --no-cache bind-tools --repository=http://dl-cdn.alpinelinux.org/alpine/edge/main
+    apk add --no-cache grep
 
 ENTRYPOINT ["/bin/bash", "-l", "-c", "/check.sh"]