vendor: update all dependencies

* Update all dependencies
  * Remove all `[[constraint]]` from Gopkg.toml
  * Add in the minimum number of `[[override]]` to build
  * Remove go get of github.com/inconshreveable/mousetrap as it is vendored
  * Update docs with new policy on constraints

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

@@ -42,6 +42,10 @@ func main() {
 		log.Fatal(err)
 	}
 
+	// Intentionally export __val fields in Fsid and Sigset_t
+	valRegex := regexp.MustCompile(`type (Fsid|Sigset_t) struct {(\s+)X__val(\s+\S+\s+)}`)
+	b = valRegex.ReplaceAll(b, []byte("type $1 struct {${2}Val$3}"))
+
 	// If we have empty Ptrace structs, we should delete them. Only s390x emits
 	// nonempty Ptrace structs.
 	ptraceRexexp := regexp.MustCompile(`type Ptrace((Psw|Fpregs|Per) struct {\s*})`)
@@ -69,12 +73,9 @@ func main() {
 	removePaddingFieldsRegex := regexp.MustCompile(`Pad_cgo_\d+`)
 	b = removePaddingFieldsRegex.ReplaceAll(b, []byte("_"))
 
-	// We refuse to export private fields on s390x
-	if goarch == "s390x" && goos == "linux" {
-		// Remove padding, hidden, or unused fields
-		removeFieldsRegex = regexp.MustCompile(`\bX_\S+`)
-		b = removeFieldsRegex.ReplaceAll(b, []byte("_"))
-	}
+	// Remove padding, hidden, or unused fields
+	removeFieldsRegex = regexp.MustCompile(`\bX_\S+`)
+	b = removeFieldsRegex.ReplaceAll(b, []byte("_"))
 
 	// Remove the first line of warning from cgo
 	b = b[bytes.IndexByte(b, '\n')+1:]