[json-lint addon] Fix broken use of var declaration

Closes #5400

Author: marijnh

addon/lint/json-lint.js

@@ -25,9 +25,7 @@ CodeMirror.registerHelper("lint", "json", function(text) {
   }
   // for jsonlint's web dist jsonlint is exported as an object with a single property parser, of which parseError
   // is a subproperty
-  if (window.jsonlint.parser) {
-    var jsonlint = window.jsonlint.parser;
-  }
+  var jsonlint = window.jsonlint.parser || window.jsonlint
   jsonlint.parseError = function(str, hash) {
     var loc = hash.loc;
     found.push({from: CodeMirror.Pos(loc.first_line - 1, loc.first_column),