fix: docker image entrypoint

changed the bindir on #445, forgot to change it in the dockerfile as well

closes #452

Signed-off-by: Carlos A Becker <caarlos0@gmail.com>

Dockerfile

@@ -1,4 +1,4 @@
 FROM alpine
 COPY nfpm_*.apk /tmp/
 RUN apk add --allow-untrusted /tmp/nfpm_*.apk
-ENTRYPOINT ["/usr/local/bin/nfpm"]
+ENTRYPOINT ["/usr/bin/nfpm"]