Update Dockerfile

Dockerfile

@@ -2,7 +2,8 @@ FROM golang:1.11.4
 
 ENV DEBIAN_FRONTEND=noninteractive 
 
-RUN 	go get -u github.com/golang/dep/cmd/dep \
+RUN 	go get github.com/MrSaints/go-ghostscript/ghostscript \
+        && go get -u github.com/golang/dep/cmd/dep \
 		&& echo deb http://deb.debian.org/debian stretch-backports main > /etc/apt/sources.list.d/backports.list \
                 && apt-get update \
                 && apt-get install -y --no-install-recommends supervisor crudini \