feat: set username to avatar alt attribute

src/component/avatar.jsx

@@ -1,7 +1,7 @@
 import React from 'react'
 
-export default ({ src, className }) => (
+export default ({ src, className, alt }) => (
   <div className={`gt-avatar ${className}`}>
-    <img src={src} alt="头像"/>
+    <img src={src} alt={alt}/>
   </div>
 )

src/component/avatar.spec.js

@@ -16,5 +16,11 @@ describe('Avatar', function () {
       .find('img').prop('src')
     ).toEqual(src)
   })
+  it('set props alt', function () {
+    const alt = 'alt'
+    expect(shallow(<Avatar alt={alt} />)
+      .find('img').prop('alt')
+    ).toEqual(alt)
+  })
 })
 

src/component/comment.jsx

@@ -62,6 +62,7 @@ export default class Comment extends Component {
         <Avatar
           className="gt-comment-avatar"
           src={comment.user && comment.user.avatar_url}
+          alt={`@${comment.user && comment.user.login}`}
         />
 
         <div className="gt-comment-content">

src/gitalk.jsx

@@ -595,7 +595,7 @@ class GitalkComponent extends Component {
     return (
       <div className="gt-header" key="header">
         {user ?
-          <Avatar className="gt-header-avatar" src={user.avatar_url} /> :
+          <Avatar className="gt-header-avatar" src={user.avatar_url} alt={`@${user.login}`} /> :
           <a className="gt-avatar-github" onMouseDown={this.handleLogin}>
             <Svg className="gt-ico-github" name="github"/>
           </a>