change the mechanism of saving txt file, use md file's way of saving

frontend/src/components/file-view/file-view.js

@@ -10,6 +10,7 @@ import CommentPanel from './comment-panel';
 import '../../css/file-view.css';
 
 const propTypes = {
+  onSaveChangedContent: PropTypes.func.isRequired,
   content: PropTypes.object.isRequired
 };
 
@@ -17,6 +18,7 @@ const { isStarred, isLocked, lockedByMe,
   repoID, filePath, enableWatermark, userNickName
 } = window.app.pageOptions;
 
+
 class FileView extends React.Component {
 
   constructor(props) {
@@ -25,7 +27,7 @@ class FileView extends React.Component {
       isStarred: isStarred,
       isLocked: isLocked,
       lockedByMe: lockedByMe,
-      isCommentPanelOpen: false
+      isCommentPanelOpen: false,
     };
   }
 
@@ -81,6 +83,7 @@ class FileView extends React.Component {
           <FileToolbar 
             isLocked={this.state.isLocked}
             lockedByMe={this.state.lockedByMe}
+            onSaveChangedContent={this.props.onSaveChangedContent}
             toggleLockFile={this.toggleLockFile}
             toggleCommentPanel={this.toggleCommentPanel}
           />