fixed a couple of typos

docs/api/net.md

@@ -136,7 +136,7 @@ Emitted when an authenticating proxy is asking for user credentials.
 
 The `callback` function is expected to be called back with user credentials:
 
-* `usrename` String
+* `username` String
 * `password` String
 
 ```JavaScript

lib/browser/api/net.js

@@ -203,7 +203,7 @@ class ClientRequest extends EventEmitter {
 
     urlRequest.on('login', (event, authInfo, callback) => {
       this.emit('login', authInfo, (username, password) => {
-        // If null or undefined usrename/password, force to empty string.
+        // If null or undefined username/password, force to empty string.
         if (username === null || username === undefined) {
           username = ''
         }