[docker] Update image to Bullseye

Dockerfile

@@ -1,25 +1,7 @@
-# Copyright (c) 2017 rockyluke
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
+FROM debian:bullseye
 
-FROM debian:jessie
-
-ENV DEBIAN_FRONTEND=noninteractive \
-    TZ=Europe/Amsterdam
-
-RUN apt-get update -qq && \
-    apt-get upgrade -qq -y && \
-    apt-get install -qq -y \
+RUN apt-get update && \
+    apt-get install --no-install-recommends -y \
       build-essential \
       bundler \
       git-core \
@@ -29,13 +11,10 @@ RUN apt-get update -qq && \
     apt-get autoclean && \
     apt-get autoremove
 
-RUN git clone https://github.com/wdhif/gitlabci-cli.git /usr/src && \
-    cd /usr/src && \
-    bundle install
-
+RUN git clone https://github.com/wdhif/gitlabci-cli.git /usr/src
 WORKDIR /usr/src
+RUN bundle install
 
 ENTRYPOINT [ "bundle", "exec", "gitlabci-cli" ]
 
 CMD [ "help" ]
-# EOF