doc: add VM2.19.1 to GM_xxxValues

Author: tophf

content/api/gm.md

@@ -120,6 +120,8 @@ let value = GM_getValue(key, defaultValue)
 
 ### GM_getValues
 
+*Since VM2.19.1*
+
 Retrieves multiple values for current script from storage.
 
 ```js
@@ -158,6 +160,8 @@ GM_setValue(key, value)
 
 ### GM_setValues
 
+*Since VM2.19.1*
+
 Writes multiple values to current script's storage.
 
 ```js
@@ -184,6 +188,8 @@ GM_deleteValue(key)
 
 ### GM_deleteValues
 
+*Since VM2.19.1*
+
 Deletes values with the specified keys in current script's storage.
 
 ```js