Suppress sbt's stderr when waiting for exit
Suppress sbt's stderr when waiting for exit

Fixes #202

This is a hacktastic way to silence some benign error output caused
by sbt when destroying a forked process.  The output appears to
come from ProcessImpl[1].

1. https://github.com/sbt/sbt/blob/v0.13.7/util/process/src/main/scala/sbt/ProcessImpl.scala#L101

earldouglas/xsbt-web-plugin,earldouglas/xsbt-web-plugin,melezov/xsbt-web-plugin