Use tomb v2, update deps, fix hang on stale connection

- Use tomb v2 to properly spawn and reap goroutines (hopefully)
- Update deps
- Fix hang on stale connection due to improper goroutine management

vendor/golang.org/x/sys/unix/dev_zos.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build zos && s390x
-// +build zos,s390x
 
 // Functions to access/create device major and minor numbers matching the
 // encoding used by z/OS.