improve code quality (#2128)

* Fix inefficient string comparison

* Fix unnecessary calls to Printf

* Canonicalize header key

* Replace `t.Sub(time.Now())` with `time.Until`

* Remove unnecessary blank (_) identifier

* Remove unnecessary use of slice

* Remove unnecessary comparison with bool

util/qson/qson_test.go

@@ -52,7 +52,7 @@ func ExampleToJSON() {
 	if err != nil {
 		panic(err)
 	}
-	fmt.Printf(string(b))
+	fmt.Print(string(b))
 	// Output: {"a":"xyz","b":{"c":456}}
 }