Remove cache of pip upgrade

Dockerfile

@@ -53,7 +53,8 @@ RUN apk upgrade --no-cache \
     uwsgi-python3 \
  && pip3 install --upgrade pip \
  && pip3 install --no-cache -r requirements.txt \
- && apk del build-dependencies
+ && apk del build-dependencies \
+ && rm -rf /root/.cache
 
 COPY --chown=searx:searx . .