Rename GetReasonFromBody() to simply Reason()

See ¹ for the customary idiomatic way of naming getters in Go.

¹: https://golang.org/doc/effective_go.html#Getters

internal/http/request.go

@@ -66,7 +66,7 @@ func Request(method string, url string, contentType string, r io.Reader, w io.Wr
 	defer res.Body.Close()
 
 	if res.StatusCode < 200 || res.StatusCode >= 300 {
-		reason, err := GetReasonFromBody(res)
+		reason, err := Reason(res)
 		if err != nil {
 			return err
 		}