build: Add unconvert linter to goclean.sh.

This modifies the goclean.sh script to include the unconvert lint tool
in the gometalinter configuration.

It also bumps the deadline to 45 seconds to give slower TravisCI
build servers more breathing room.

goclean.sh

@@ -17,6 +17,7 @@ test -z "$(gometalinter --disable-all \
 --enable=golint \
 --enable=vet \
 --enable=gosimple \
+--enable=unconvert \
 --deadline=20s $(glide novendor) | grep -v 'ALL_CAPS\|OP_' 2>&1 | tee /dev/stderr)"
 env GORACE="halt_on_error=1" go test -v -race -tags rpctest $(glide novendor)