message: docs: add curl to Ubuntu deps
  Following PR the build uses `curl` instead of `wget`. As a
  result, package curl has become a dependency.
  Risk Level: Low
  Testing: Bazel build on Ubuntu 18.04
  Docs Changes: N/A
  Release Notes: N/A
diff: @@ -27,7 +27,7 @@ up-to-date with the latest security patches. See
  for how to update or override dependencies.
  1. Install the latest version of [Bazel](https://bazel.build/versions/master/docs/install.html) in your environment.
  -2. Install external dependencies libtool, cmake, ninja, and realpath libraries separately.
  +2. Install external dependencies libtool, cmake, ninja, realpath and curl libraries separately.
  On Ubuntu, run the following commands:
  ```
  apt-get install libtool
  @@ -36,6 +36,7 @@ On Ubuntu, run the following commands:
  apt-get install clang-format-5.0
  apt-get install automake
  apt-get install ninja-build
  + apt-get install curl
  ```
  On Fedora (maybe also other red hat distros), run the following:
  