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/windows/dll_windows.go

@@ -65,7 +65,7 @@ func LoadDLL(name string) (dll *DLL, err error) {
 	return d, nil
 }
 
-// MustLoadDLL is like LoadDLL but panics if load operation failes.
+// MustLoadDLL is like LoadDLL but panics if load operation fails.
 func MustLoadDLL(name string) *DLL {
 	d, e := LoadDLL(name)
 	if e != nil {