vendor: Mega update all dependencies

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4080

vendor/github.com/kardianos/osext/osext_go18.go

@@ -0,0 +1,9 @@
+//+build go1.8,!openbsd
+
+package osext
+
+import "os"
+
+func executable() (string, error) {
+	return os.Executable()
+}