upgrade gradle to version 6

slave/Dockerfile

@@ -7,6 +7,7 @@ ARG ICEVER=ice36-devel
 ARG BRANCH=yourbranch
 ARG NAME=yourname
 
+ARG GRADLEVER=6.9.3
 
 # skip some omero-install
 RUN echo 'export container=docker' > /etc/profile.d/docker.sh
@@ -62,10 +63,10 @@ RUN yum -y install postgresql10-server postgresql10 \
 
 # gradle
 RUN cd /opt && \
-    curl -fSLO https://services.gradle.org/distributions/gradle-5.2.1-bin.zip && \
-    unzip gradle-5.2.1-bin.zip && \
-    rm gradle-5.2.1-bin.zip && \
-    ln -s /opt/gradle-5.2.1/bin/gradle /usr/local/bin/gradle
+    curl -fSLO https://services.gradle.org/distributions/gradle-GRADLEVER-bin.zip && \
+    unzip gradle-GRADLEVER-bin.zip && \
+    rm gradle-GRADLEVER-bin.zip && \
+    ln -s /opt/gradle-GRADLEVER/bin/gradle /usr/local/bin/gradle
 
 ENV JAVA_HOME /usr/lib/jvm/java-11-openjdk
 ENV PATH=$JAVA_HOME/bin:$PATH