Fix typo in documentation for map_values (#3035)

* Fix typo in documentation for map_values

"map_value(f)" -> "map_values(f)"

* map_value => map_values also in the devolpment manual

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Co-authored-by: Emanuele Torre <torreemanuele6@gmail.com>

docs/content/manual/manual.yml

@@ -1007,7 +1007,7 @@ sections:
           `($x|f)` for each value, $x, in the input array or object,
           but `map_values(f)` only uses `first($x|f)`.
 
-          Specifically, for object inputs, `map_value(f)` constructs
+          Specifically, for object inputs, `map_values(f)` constructs
           the output object by examining in turn the value of
           `first(.[$k]|f)` for each key, $k, of the input.  If this
           expression produces no values, then the corresponding key