fix(readme): add espower to example codes

Author: watilde

README.md

@@ -27,7 +27,11 @@ module.exports = function(config) {
 
     files: [
       '*.js'
-    ]
+    ],
+
+    preprocessors: {
+      'test/**/*.spec.js': ['espower']
+    }
   });
 };
 ```
@@ -45,6 +49,10 @@ module.exports = function(config) {
       '*.js'
     ],
 
+    preprocessors: {
+      'test/**/*.spec.js': ['espower']
+    },
+
     client: {
       assert: {
         output: {