fix: requested grammar fixes

Author: raphael-goetz

definitions/standard/runtime_definition/object/std_object_keys.proto.json

@@ -22,7 +22,7 @@
       "documentation": [
         {
           "code": "en-US",
-          "content": "Returns an list of all the keys (property names) of the given object."
+          "content": "Returns a list of all the keys (property names) of the given object."
         }
       ]
     }
@@ -54,13 +54,13 @@
   "description": [
     {
       "code": "en-US",
-      "content": "Retrieves all the keys from the given object as an list of text values."
+      "content": "Retrieves all the keys from the given object as a list of text values."
     }
   ],
   "documentation": [
     {
       "code": "en-US",
-      "content": "Returns an list containing all enumerable property names (keys) of the specified object."
+      "content": "Returns a list containing all enumerable property names (keys) of the specified object."
     }
   ],
   "alias": [