Dockerfile fix

@@ -8,6 +8,7 @@ COPY ./cmd/pdftopng cmd/pdftopng
 COPY ./go.mod go.mod
 COPY ./go.mod go.mod
 COPY ./go.sum go.sum
 COPY ./go.sum go.sum
 COPY ./main.go main.go
 COPY ./main.go main.go
+RUN chmod +x cmd/pdftopng
 RUN ["ln","-sf","/usr/share/zoneinfo/Asia/Shanghai","/etc/localtime"]
 RUN ["ln","-sf","/usr/share/zoneinfo/Asia/Shanghai","/etc/localtime"]
 ENV GO111MODULE on
 ENV GO111MODULE on
 ENV GOPROXY https://goproxy.cn
 ENV GOPROXY https://goproxy.cn