remove clean target folders script

not needed (nor is is a good implementation)
for future reference:
#!/bin/sh
find . -type d -name 'target' -prune -exec rm -rf {} \;
update to sbt 0.13.6
simplify resolvers

no snapshots!
update deps

the very latest specs2 was not used as it has scalaz stream as a dependency
attempt to quieten sbt output in Travis