doc: runtime deprecate util.isString

Author: marco-ippolito

doc/api/deprecations.md

@@ -1242,6 +1242,9 @@ The [`util.isRegExp()`][] API is deprecated.
 
 <!-- YAML
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/50487
+    description: Runtime deprecation.
   - version:
     - v6.12.0
     - v4.8.6
@@ -1254,7 +1257,7 @@ changes:
     description: Documentation-only deprecation.
 -->
 
-Type: Documentation-only
+Type: Runtime
 
 The [`util.isString()`][] API is deprecated.
 

lib/util.js

@@ -388,7 +388,7 @@ module.exports = {
   isNull: deprecate(isNull, 'The `util.isNull API is deprecated.', 'DEP0050'),
   isNullOrUndefined: deprecate(isNullOrUndefined, 'The `util.isNullOrUndefined API is deprecated.', 'DEP0051'),
   isNumber: deprecate(isNumber, 'The `util.isNumber API is deprecated.', 'DEP0052'),
-  isString,
+  isString: deprecate(isString, 'The `util.isString API is deprecated.', 'DEP0056'),
   isSymbol,
   isUndefined,
   isRegExp: deprecate(types.isRegExp, 'The `util.isRegExp API is deprecated.', 'DEP0055'),