make variable for version

Author: Adrian Cole

zipkin/Dockerfile

@@ -16,13 +16,14 @@ FROM alpine
 
 ENV USER anuraaga
 ENV BRANCH elasticsearch-armeria
+ENV VERSION SNAPSHOT
 
 # Add environment settings for supported storage types
 COPY zipkin/ /zipkin/
 WORKDIR /zipkin
 
 RUN apk add unzip curl --no-cache && \
-    curl -SL https://jitpack.io/com/github/$USER/zipkin/zipkin-server/$BRANCH-SNAPSHOT/zipkin-server-$BRANCH-SNAPSHOT-exec.jar > zipkin-server.jar && \
+    curl -SL https://jitpack.io/com/github/$USER/zipkin/zipkin-server/$BRANCH-$VERSION/zipkin-server-$BRANCH-$VERSION-exec.jar > zipkin-server.jar && \
     # don't break when unzip finds an extra header https://github.com/openzipkin/zipkin/issues/1932
     unzip zipkin-server.jar ; \
     rm zipkin-server.jar && \