update java runtime security policy

dockerfiles/judger/Dockerfile

@@ -18,4 +18,5 @@ RUN git clone https://github.com/quark-zju/lrun.git
 RUN cd lrun && make install
 RUN mkdir -p /var/judger/run/ && mkdir /var/judger/test_case/ && mkdir /var/judger/code/
 RUN chmod -R 777 /var/judger/run/
+COPY policy /var/judger/run/
 WORKDIR /var/judger/code/

dockerfiles/judger/policy

@@ -0,0 +1,3 @@
+grant {
+    permission java.io.FilePermission "/tmp", "read";
+};