Get Swagger-UI from https://github.com/swagger-api/swagger-ui/releases
e.g.
# wget https://github.com/swagger-api/swagger-ui/archive/v3.24.3.tar.gz
# tar xf v3.24.3.tar.gz
# cd swagger-ui-3.24.3/dist
# ln -s ../../echopb/echo.swagger.json
# python3 -m http.server