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/gccgo_c.c

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build gccgo && !aix && !hurd
-// +build gccgo,!aix,!hurd
 
 #include <errno.h>
 #include <stdint.h>