Change "extentions" to "extensions" in require-extension

While working on a different rule, I noticed a small typo here and
thought it was worth fixing.

Author: lencioni

lib/rules/require-extension.js

@@ -11,7 +11,7 @@ var path = require('path');
 // ------------------------------------------------------------------------------
 
 var DEFAULTS = {
-  extentions: ['.jsx']
+  extensions: ['.jsx']
 };
 
 var PKG_REGEX = /^[^\.]((?!\/).)*$/;
@@ -38,11 +38,11 @@ module.exports = function(context) {
     return path.extname(id || '');
   }
 
-  function getExtentionsConfig() {
-    return context.options[0] && context.options[0].extensions || DEFAULTS.extentions;
+  function getExtensionsConfig() {
+    return context.options[0] && context.options[0].extensions || DEFAULTS.extensions;
   }
 
-  var forbiddenExtensions = getExtentionsConfig().reduce(function (extensions, extension) {
+  var forbiddenExtensions = getExtensionsConfig().reduce(function (extensions, extension) {
     extensions[extension] = true;
     return extensions;
   }, Object.create(null));