Add psmisc package to the docker (for killall)

Dockerfile.in

@@ -1,6 +1,6 @@
 FROM ubuntu:18.04
 RUN apt update
-RUN apt install -y python3 python3-pip python3-dev build-essential screen sudo
+RUN apt install -y python3 python3-pip python3-dev build-essential screen sudo psmisc
 RUN pip3 install merklelib
 RUN pip3 install pynacl
 RUN groupadd -g GROUP_ID walkingo