docs: fix sample code that uses non-existent methods

Author: kenjis

user_guide_src/source/libraries/time.rst

@@ -334,9 +334,9 @@ thrown.
 ::
 
     $time = $time->setYear(2017);
-    $time = $time->setMonthNumber(4); // April
-    $time = $time->setMonthLongName('April');
-    $time = $time->setMonthShortName('Feb'); // February
+    $time = $time->setMonth(4);     // April
+    $time = $time->setMonth('April');
+    $time = $time->setMonth('Feb'); // February
     $time = $time->setDay(25);
     $time = $time->setHour(14); // 2:00 pm
     $time = $time->setMinute(30);