Switch Docker base image to Debian (closes snowplow#283)

Dockerfile

@@ -1,18 +1,16 @@
-FROM centos:8
-RUN cd /etc/yum.repos.d/
-RUN sed -i 's/mirrorlist/#mirrorlist/g' /etc/yum.repos.d/CentOS-*
-RUN sed -i 's|#baseurl=http://mirror.centos.org|baseurl=http://vault.centos.org|g' /etc/yum.repos.d/CentOS-*
+FROM debian:bullseye-slim
+
+RUN apt-get update && apt-get install -y --no-install-recommends make build-essential libssl-dev zlib1g-dev libbz2-dev libreadline-dev \
+    libsqlite3-dev wget curl llvm libncurses5-dev xz-utils tk-dev libxml2-dev libxmlsec1-dev libffi-dev liblzma-dev \
+    mecab-ipadic-utf8 git ca-certificates
 
-RUN yum -y install wget
-RUN yum install -y epel-release
-RUN yum -y install git tar gcc make bzip2 openssl openssl-devel patch gcc-c++ libffi-devel sqlite-devel
-RUN git clone https://github.com/yyuu/pyenv.git ~/.pyenv
 ENV HOME /root
 ENV PYENV_ROOT $HOME/.pyenv
 ENV PATH $PYENV_ROOT/shims:$PYENV_ROOT/bin:$PATH
+RUN git clone --depth=1 https://github.com/pyenv/pyenv.git $PYENV_ROOT
+RUN git clone https://github.com/pyenv/pyenv-virtualenv.git $PYENV_ROOT/plugins/pyenv-virtualenv
 
 RUN pyenv install 3.5.10 && pyenv install 3.6.14 && pyenv install 3.7.11 && pyenv install 3.8.11 && pyenv install 3.9.6 && pyenv install 3.10.1
-RUN git clone https://github.com/pyenv/pyenv-virtualenv.git ~/.pyenv/plugins/pyenv-virtualenv
 
 WORKDIR /app
 COPY . .