message: Fix outdated link to "hello world" examples
  As of the examples/helloworld directory no longer exists
diff: @@ -49,7 +49,7 @@ the Bazel team and makes it easy to ensure usage of a version of Bazel that's
  compatible with the project.
  As a starting point, the [`hello world
  -examples`](https://github.com/google/tink/tree/master/examples/helloworld)
  +examples`](https://github.com/google/tink/tree/master/examples)
  demonstrate performing simple tasks using Tink in a variety of languages.
  ## Overview
  