update(): alpine 3.7

Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.6
+FROM alpine:3.7
 
 LABEL description "PostfixAdmin is a web based interface used to manage mailboxes" \
       maintainer="Hardware <[email protected]>"
@@ -10,7 +10,7 @@ ARG VERSION=3.1
 ARG GPG_SHORTID="0xC6A682EA63C82F1C"
 ARG GPG_FINGERPRINT="70CA A060 DE04 2AAE B1B1  5196 C6A6 82EA 63C8 2F1C"
 
-RUN echo "@community https://nl.alpinelinux.org/alpine/v3.6/community" >> /etc/apk/repositories \
+RUN echo "@community https://nl.alpinelinux.org/alpine/v3.7/community" >> /etc/apk/repositories \
  && apk -U upgrade \
  && apk add -t build-dependencies \
     ca-certificates \
@@ -29,12 +29,14 @@ RUN echo "@community https://nl.alpinelinux.org/alpine/v3.6/community" >> /etc/a
  && PFA_TARBALL="postfixadmin-${VERSION}.tar.gz" \
  && wget -q https://downloads.sourceforge.net/project/postfixadmin/postfixadmin/postfixadmin-${VERSION}/${PFA_TARBALL} \
  && wget -q https://downloads.sourceforge.net/project/postfixadmin/postfixadmin/postfixadmin-${VERSION}/${PFA_TARBALL}.asc \
- && gpg --keyserver pgp.mit.edu --recv-keys ${GPG_SHORTID} || \
+ && ( \
+    gpg --keyserver pgp.mit.edu --recv-keys ${GPG_SHORTID} || \
     gpg --keyserver keyserver.pgp.com --recv-keys ${GPG_SHORTID} || \
     gpg --keyserver ha.pool.sks-keyservers.net --recv-keys ${GPG_SHORTID} \
+    ) \
  && FINGERPRINT="$(LANG=C gpg --verify ${PFA_TARBALL}.asc ${PFA_TARBALL} 2>&1 | sed -n "s#Primary key fingerprint: \(.*\)#\1#p")" \
- && if [ -z "${FINGERPRINT}" ]; then echo "Warning! Invalid GPG signature!" && exit 1; fi \
- && if [ "${FINGERPRINT}" != "${GPG_FINGERPRINT}" ]; then echo "Warning! Wrong GPG fingerprint!" && exit 1; fi \
+ && if [ -z "${FINGERPRINT}" ]; then echo "ERROR: Invalid GPG signature!" && exit 1; fi \
+ && if [ "${FINGERPRINT}" != "${GPG_FINGERPRINT}" ]; then echo "ERROR: Wrong GPG fingerprint!" && exit 1; fi \
  && mkdir /postfixadmin && tar xzf ${PFA_TARBALL} -C /postfixadmin && mv /postfixadmin/postfixadmin-$VERSION/* /postfixadmin \
  && apk del build-dependencies \
  && rm -rf /var/cache/apk/* /tmp/* /root/.gnupg /postfixadmin/postfixadmin-$VERSION*