message: Docs: corrected outdated command
  Corrected the command to build an envoy docker image from source.
  Additional Description: N/A
  Risk Level: N/A
  Testing: N/A
  Docs Changes: Building an Envoy Docker image - Updated step 2
  Release Notes: N/A
diff: @@ -26,7 +26,7 @@ of the software used to build it.::
  $ pwd
  src/envoy/
  - $ docker build -f ci/Dockerfile-envoy-image -t envoy .
  + $ docker build -f ci/Dockerfile-envoy -t envoy .
  Now you can use this ``envoy`` image to build the any of the sandboxes if you change
  the ``FROM`` line in any Dockerfile.
  