fix(docker): Add mime.types file

Uses the package mailcap from alpine as a source for /etc/mime.types
which is required by golang.org/pkg/mime on unix systems.

Dockerfile

@@ -1,8 +1,10 @@
-FROM alpine:latest as certs
+FROM alpine:latest as alpine
 RUN apk --update add ca-certificates
+RUN apk --update add mailcap
 
 FROM scratch
-COPY --from=certs /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/ca-certificates.crt
+COPY --from=alpine /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/ca-certificates.crt
+COPY --from=alpine /etc/mime.types /etc/mime.types
 
 VOLUME /srv
 EXPOSE 80