Fix docker build problem on jetty

.travis.yml

@@ -9,15 +9,15 @@ after_success:
   - docker login  -u $DOCKER_LOGIN -p $DOCKER_PASSWORD
   - if [ "$TRAVIS_BRANCH" == "master" ]; then
 
-    docker build -t plantuml/plantuml-server:jetty -f Dockerfile.jetty . ;
-    docker build -t plantuml/plantuml-server:tomcat -f Dockerfile.tomcat . ;
+    docker build --pull -t plantuml/plantuml-server:jetty -f Dockerfile.jetty . ;
+    docker build --pull -t plantuml/plantuml-server:tomcat -f Dockerfile.tomcat . ;
     docker tag plantuml/plantuml-server:jetty plantuml/plantuml-server:latest ;
 
     docker push plantuml/plantuml-server:tomcat;
     docker push plantuml/plantuml-server:jetty;
     docker push plantuml/plantuml-server:latest;
 
-    docker build -t plantuml/plantuml-server:armv8a -f Dockerfile.armv8a . ;
+    docker build --pull -t plantuml/plantuml-server:armv8a -f Dockerfile.armv8a . ;
     docker push plantuml/plantuml-server:armv8a;
 
     fi

Dockerfile.jetty

 FROM maven:3-jdk-8 AS builder
 
-RUN apt-get update && apt-get install -y --no-install-recommends graphviz fonts-wqy-zenhei && rm -rf /var/lib/apt/lists/*
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends graphviz fonts-wqy-zenhei && \
+    apt-get clean
 
 COPY pom.xml /app/
 COPY src /app/src/
@@ -14,9 +16,13 @@ RUN mvn package
 FROM jetty
 MAINTAINER D.Ducatel
 
+USER root
+
 RUN apt-get update && \
     apt-get install -y --no-install-recommends graphviz fonts-wqy-zenhei && \
-    rm -rf /var/lib/apt/lists/*
+    apt-get clean
+
+USER jetty
 
 COPY --from=builder /app/target/plantuml.war /var/lib/jetty/webapps/ROOT.war
 

Dockerfile.tomcat

 FROM maven:3-jdk-8 AS builder
 
-RUN apt-get update && apt-get install -y --no-install-recommends graphviz fonts-wqy-zenhei && rm -rf /var/lib/apt/lists/*
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends graphviz fonts-wqy-zenhei && \
+    apt-get clean
 
 COPY pom.xml /app/
 COPY src /app/src/
@@ -16,7 +18,7 @@ MAINTAINER D.Ducatel
 
 RUN apt-get update && \
     apt-get install -y --no-install-recommends graphviz fonts-wqy-zenhei && \
-    rm -rf /var/lib/apt/lists/*
+    apt-get clean
 
 RUN rm -rf /usr/local/tomcat/webapps/ROOT
 COPY --from=builder /app/target/plantuml.war /usr/local/tomcat/webapps/ROOT.war