allow disallowMultipleVarDecl to be false as to override preset

I inherit from the preset "google", but I want to allow multiple vars. Unless I'm missing something I think it would be best to remove that assertion otherwise you cannot override the extended preset.

lib/rules/disallow-multiple-var-decl.js

@@ -9,10 +9,6 @@ module.exports.prototype = {
             typeof disallowMultipleVarDecl === 'boolean',
             'disallowMultipleVarDecl option requires boolean value'
         );
-        assert(
-            disallowMultipleVarDecl === true,
-            'disallowMultipleVarDecl option requires true value or should be removed'
-        );
     },
 
     getOptionName: function() {