Old kafka URL is dead, replace with new one

for upstream 0.8.1.1 release

we should find a way to make this not break on each new upstream release
Merge pull request #83 from eapache/fix-travis

Old kafka URL is dead, replace with new one
Fix two minor bugs in producer.go

 - Remove a second superfluous call to bp.flush when bp.flushNow is
   triggered.
 - Release delivery lock after use instead of deferring until end of
   function.