drools-pdp docker build fail

after official jre 2.2.0 released
there is no /root/.cache exist
based on jenkins build

Issue-ID: POLICY-2999
Change-Id: I6c7db9dce3269bdcd26016d4049364bc72310dac
Signed-off-by: Taka Cho <takamune.cho@att.com>
diff --git a/packages/docker/src/main/docker/Dockerfile b/packages/docker/src/main/docker/Dockerfile
index 2c3c3aa..195780c 100644
--- a/packages/docker/src/main/docker/Dockerfile
+++ b/packages/docker/src/main/docker/Dockerfile
@@ -50,8 +50,7 @@
     && update-alternatives --install /usr/bin/pip pip /usr/bin/pip3 1 \
     && pip install --no-cache-dir --upgrade setuptools http-prompt \
     && pip uninstall -y httpie \
-    && pip install --no-cache-dir httpie==1.0.3 \
-    && rm -r /root/.cache
+    && pip install --no-cache-dir httpie==1.0.3
 
 RUN mkdir -p $POLICY_CONFIG $POLICY_LOGS $POLICY_INSTALL_INIT && \
     chown -R policy:policy $POLICY_HOME $POLICY_LOGS $POLICY_INSTALL