War file location fix

Fix for getting the war file from the right location.
Steps for validation:

git clone https://github.com/apache/roller.git
cd roller
docker build -t rollerdocker .
diff --git a/Dockerfile b/Dockerfile
index 53affc4..2dcbcd4 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -62,7 +62,7 @@
 # install Roller WAR as ROOT.war, create data dirs
 WORKDIR /usr/local/roller
-COPY --from=builder /project/app/target/roller.war /usr/local/tomcat/webapps/ROOT.war
+COPY --from=builder /tmp/roller/app/target/roller.war /usr/local/tomcat/webapps/ROOT.war
 RUN mkdir -p data/mediafiles data/searchindex
 # download PostgreSQL and MySQL drivers plus Mail and Activation JARs
@@ -81,4 +81,4 @@
 RUN chmod -R g+rw /usr/local/tomcat
 WORKDIR /usr/local/tomcat
-ENTRYPOINT /usr/local/tomcat/bin/entry-point.sh
\ No newline at end of file
+ENTRYPOINT /usr/local/tomcat/bin/entry-point.sh