Bump to tokio 0.2.16. (#9467)
Bump to tokio 0.2.16. (#9467)

### Problem

tokio has a new release that we're not on.

### Solution

Hop on it.

[ci skip-jvm-tests]  # No JVM changes made.
jsirois/pants,pantsbuild/pants,pantsbuild/pants,tdyas/pants,tdyas/pants,jsirois/pants,benjyw/pants,tdyas/pants,benjyw/pants,benjyw/pants,tdyas/pants,benjyw/pants,benjyw/pants,tdyas/pants,benjyw/pants,pantsbuild/pants,pantsbuild/pants,jsirois/pants,tdyas/pants,pantsbuild/pants,pantsbuild/pants,tdyas/pants,tdyas/pants,tdyas/pants,pantsbuild/pants,benjyw/pants