Updated rugged dependency to avoid flaky 0.21.0
Updated rugged dependency to avoid flaky 0.21.0

0.19.0 compiles on OS X while 0.21.0 does not.
mvz/pronto,jhass/pronto,prontolabs/pronto,Zauberstuhl/pronto,HaiTo/pronto,gussan/pronto,treble37/pronto,mmozuras/pronto,aergonaut/pronto