fix(test): Fix presubmit with python version upgrade (kubeflow#5033)

* Fix presubmit with python version upgrade

* Update Dockerfile

Co-authored-by: Yuan (Bob) Gong <4957653+Bobgy@users.noreply.github.com>

backend/Dockerfile

@@ -8,7 +8,7 @@ RUN go mod vendor
 RUN GO111MODULE=on go build -o /bin/apiserver backend/src/apiserver/*.go
 
 # 2. Compile preloaded pipeline samples
-FROM python:3.5 as compiler
+FROM python:3.7 as compiler
 RUN apt-get update -y && apt-get install --no-install-recommends -y -q default-jdk python3-setuptools python3-dev jq
 RUN wget https://bootstrap.pypa.io/get-pip.py && python3 get-pip.py
 COPY backend/requirements.txt .

backend/update_requirements.sh

@@ -3,7 +3,7 @@
 # Usage: update_requirements.sh <requirements.in >requirements.txt
 
 set -euo pipefail
-IMAGE=${1:-"python:3.5"}
+IMAGE=${1:-"python:3.7"}
 docker run --interactive --rm "$IMAGE" sh -c '
   python3 -m pip install pip setuptools --upgrade --quiet
   python3 -m pip install pip-tools==5.4.0 --quiet