fix: remove quoted strings (hadolint)

Dockerfile

@@ -1,23 +1,22 @@
-FROM "ubuntu:18.04"
+FROM ubuntu:18.04
 LABEL maintainer="Julien Cabillot <dockerimages@cabillot.eu>"
 
-RUN export DEBIAN_FRONTEND="noninteractive" && \
-    export BUILD_PACKAGES="git-core" && \
+RUN export DEBIAN_FRONTEND=noninteractive && \
+    export BUILD_PACKAGES=git-core && \
     export RUNTIME_PACKAGES="python bsdmainutils curl python-six" && \
     apt-get -qq update && \
     apt-get -qq --yes install ${BUILD_PACKAGES} ${RUNTIME_PACKAGES} && \
-    git clone "https://github.com/jvehent/cipherscan.git" && \
+    git clone https://github.com/jvehent/cipherscan.git && \
     /cipherscan/cscan.sh -l && \
     apt-get -qq --yes remove --purge ${BUILD_PACKAGES} && \
     apt-get -qq --yes autoremove --purge && \
     apt-get -qq --yes clean all && \
-    rm -rf "/usr/share/doc/"* \
-           "/usr/src/"* \
-           "/var/cache/"* \
-           "/var/lib/apt/lists/"* \
-           "/var/log/"{apt/*,dpkg.log} \
-           "/tmp/"*
+    rm -rf /usr/share/doc/* \
+           /usr/src/* \
+           /var/cache/* \
+           /var/lib/apt/lists/* \
+           /var/log/{apt/*,dpkg.log} \
+           /tmp/*
 
-
-ENTRYPOINT ["/cipherscan/cipherscan"]
-CMD ["--help"]
+ENTRYPOINT [ "/cipherscan/cipherscan" ]
+CMD [ "--help" ]