disallowDanglingUnderscores: Corrected rule name in assert message

Fixes #1139
Closes gh-1140

lib/rules/disallow-dangling-underscores.js

@@ -63,7 +63,7 @@ module.exports.prototype = {
             typeof identifiers !== 'object' ||
             Array.isArray(identifiers.allExcept) &&
             typeof identifiers.allExcept[0] === 'string',
-            'Property `allExcept` in requireSpaceAfterLineComment should be an array of strings'
+            'Property `allExcept` in disallowDanglingUnderscores should be an array of strings'
         );
 
         var isTrue = identifiers === true;