build: update proxy agent to fix CVE vulnerabilities. Fixes #4531 (#4606)

Author: Bobgy

proxy/Dockerfile

@@ -13,12 +13,11 @@
 # limitations under the License.
 
 # Pin to a specific version of invert proxy agent
-FROM gcr.io/inverting-proxy/agent@sha256:d0a06a247bb443f9528356a1341cadfa4c4479a034097ef9ed8cf200c6383ec0
+FROM gcr.io/inverting-proxy/agent@sha256:9817c740a3705e4bf889e612c071686a8cb3cfcfe9ad191c570a295c37316ff0
 
 RUN apt-get update && apt-get install -y curl jq python-pip
 RUN pip install requests
-RUN curl https://raw.githubusercontent.com/requests/requests/master/LICENSE --output /opt/license.txt
- 
+
 # Install gcloud SDK
 RUN curl https://dl.google.com/dl/cloudsdk/release/google-cloud-sdk.tar.gz > /tmp/google-cloud-sdk.tar.gz
 RUN mkdir -p /usr/local/gcloud