docker: switch to Go 1.4 and add ca-certificates package

Dockerfile

 ### Build Image
-FROM golang:1.13-buster
+FROM golang:1.14-buster
 MAINTAINER Christian Pointner <equinox@helsinki.at>
 
 RUN set -e \
@@ -24,7 +24,7 @@ MAINTAINER Christian Pointner <equinox@helsinki.at>
 
 RUN set -e \
   && apt-get update -q \
-  && apt-get install -y -q --no-install-recommends ffmpeg \
+  && apt-get install -y -q --no-install-recommends ffmpeg ca-certificates \
   && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 
 RUN set -e \