absolute path to entrypoint

Make the kustomize container tolerant of alternative working directory. 
Mounting my project and making it the working directory will now work.

ie. docker run -w /pkg -v $(shell pwd):/pkg kustomize version

kustomize.Dockerfile

@@ -17,4 +17,4 @@ FROM alpine
 RUN apk add git openssh
 COPY --from=builder /build/kustomize /app/
 WORKDIR /app
-ENTRYPOINT ["./kustomize"]
+ENTRYPOINT ["/app/kustomize"]