Log Message:
Update ruby-raindrops to 0.19.0.

=== raindrops 0.19.0 - Rack 2.x middleware compatibility / 2017-08-09 23:52 UTC

  This release fixes Rack 2.x compatibility for the few users of
  Raindrops::Middleware
  <https://bogomips.org/raindrops/Raindrops/Middleware.html>.
  Thanks to Dmytro Shteflyuk for this release.

  No need to upgrade unless you use Raindrops::Middleware with
  Rack 2.x.

  There's also a few minor, inconsequential cleanups.

  Dmytro Shteflyuk (1):
        Properly override respond_to? in Raindrops::Middleware::Proxy

  Eric Wong (2):
        Ruby thread compatibility updates
        tcp_info: remove unnecessary extconf.h include