Bump alpine from 3.7 to 3.8 (#29)

Bumps alpine from 3.7 to 3.8.

Signed-off-by: dependabot[bot] <support@dependabot.com>

Dockerfile

@@ -3,7 +3,7 @@ ARG CFSSL_VERSION=1.3.2
 FROM cfssl/cfssl:${CFSSL_VERSION} as cfssl
 
 # Install remaining packages
-FROM alpine:3.7
+FROM alpine:3.8
 ENV INSTALL_PATH=/packages/bin
 ENV PATH=${INSTALL_PATH}:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
 RUN mkdir -p ${INSTALL_PATH}