chore: use go 1.16 (#449)

* chore: use go 1.16 and gofmt accordingly

* chore: also update examples and tuts to go 1.16

examples/chat/main.go

@@ -22,8 +22,10 @@ func main() {
 	}
 }
 
-type tickMsg struct{}
-type errMsg error
+type (
+	tickMsg struct{}
+	errMsg  error
+)
 
 type model struct {
 	viewport    viewport.Model