Update Dockerfile

Packages 'git' and 'ca-certificates' not required anymore, since Dockerfile is within the source code.

docker/Dockerfile

@@ -1,5 +1,5 @@
 # based on Docker image created by
-# Adrián Parilli <a.parilli@staffwerke.de>
+# Adrián Parilli <adrian.parilli@staffwerke.de>
 # Uses parent directory as context:
 # git clone https://github.com/abbbi/virtnbdbackup
 # cd virtnbdbackup
@@ -21,10 +21,10 @@ COPY . /tmp/build/
 RUN \
 apt-get update && \
 apt-get install -y --no-install-recommends \
-openssh-client ca-certificates git python3-all python3-libnbd python3-libvirt python3-lz4 python3-setuptools python3-tqdm qemu-utils python3-lxml python3-paramiko python3-colorlog && \
+openssh-client python3-all python3-libnbd python3-libvirt python3-lz4 python3-setuptools python3-tqdm qemu-utils python3-lxml python3-paramiko python3-colorlog && \
 cd /tmp/build/ && python3 setup.py install && cd .. && \
-apt-get purge -y git ca-certificates && apt-get -y autoremove --purge && apt-get clean && \
-rm -rf /var/lib/apt/lists/* /tmp/* /virtnbdbackup
+apt-get -y autoremove --purge && apt-get clean && \
+rm -rf /var/lib/apt/lists/* /tmp/*
 
 # Default folder:
 WORKDIR /