Add missing backslash

Author: hslatman

docker/Dockerfile.debian

@@ -31,7 +31,7 @@ RUN apt-get update \
         && apt-get upgrade -y \
         && apt-get install -y --no-install-recommends curl \
         && addgroup --gid ${STEPGID} step \
-        && adduser --disabled-password --uid ${STEPUID} --gid ${STEPGID} step
+        && adduser --disabled-password --uid ${STEPUID} --gid ${STEPGID} step \
         && chown step:step /home/step
 
 COPY --from=builder /src/bin/step "/usr/local/bin/step"