add scrollbar file explorer if needed

src/app/panels/file-panel.js

@@ -33,8 +33,9 @@ var css = csjs`
     width             : 100%;
   }
   .menu               {
-    display           : flex;
-    flex-direction    : row;
+    height            : 2em;
+    margin-top        : 0.5em;
+    flex-shrink       : 0;
   }
   .newFile            {
     padding           : 10px;
@@ -84,6 +85,9 @@ var css = csjs`
   .treeview {
     background-color  : ${styles.colors.white};
   }
+  .treeviews {
+    overflow-y        : auto;
+  }
   .dragbar            {
     position          : absolute;
     top               : 37px;
@@ -151,9 +155,11 @@ function filepanel (appAPI, filesProvider) {
               <i class="websocketconn fa fa-link" title="Connect to Localhost"></i>
             </span>
           </div>
+          <div class=${css.treeviews}>
             <div class=${css.treeview}>${fileExplorer.init()}</div>
             <div class="filesystemexplorer ${css.treeview}"></div>
           </div>
+        </div>
         ${dragbar}
       </div>
     `