add bash shell as default (#10)

Dockerfile.ubuntu-1804

@@ -3,6 +3,8 @@ FROM ubuntu:18.04
 LABEL maintainer="LinuxGSM <[email protected]>"
 ARG DEBIAN_FRONTEND=noninteractive
 
+SHELL ["/bin/bash", "-o", "pipefail", "-c"]
+
 # Install SteamCMD
 RUN echo "**** Install SteamCMD ****" \
   && echo steam steam/question select "I AGREE" | debconf-set-selections \

Dockerfile.ubuntu-2004

@@ -3,6 +3,8 @@ FROM ubuntu:20.04
 LABEL maintainer="LinuxGSM <[email protected]>"
 ARG DEBIAN_FRONTEND=noninteractive
 
+SHELL ["/bin/bash", "-o", "pipefail", "-c"]
+
 # Install SteamCMD
 RUN echo "**** Install SteamCMD ****" \
   && echo steam steam/question select "I AGREE" | debconf-set-selections \

Dockerfile.ubuntu-2204

@@ -2,6 +2,7 @@ FROM ubuntu:22.04
 
 LABEL maintainer="LinuxGSM <[email protected]>"
 ARG DEBIAN_FRONTEND=noninteractive
+SHELL ["/bin/bash", "-o", "pipefail", "-c"]
 
 # Install SteamCMD
 RUN echo "**** Install SteamCMD ****" \