Fix typo in README (#128)

meain · SBoudrias · commit 3e5cea009be6 · 2017-10-23T12:31:11.000+08:00
diff --git a/readme.md b/readme.md
@@ -23,7 +23,7 @@ $ npm install update-notifier
 ```
 
 
-## Usafe
+## Usage
 
 ### Simple
 
