getting-started: fixed open folder link (#12857)

The commit updates the `open folder` link when no recent workspaces are
present to prompt users to open a folder instead of a workspace file.

Signed-off-by: vince-fugnitto <vincent.fugnitto@ericsson.com>

Author: vince-fugnitto

packages/getting-started/src/browser/getting-started-widget.tsx

@@ -270,8 +270,8 @@ export class GettingStartedWidget extends ReactWidget {
                 <a
                     role={'button'}
                     tabIndex={0}
-                    onClick={this.doOpenWorkspace}
-                    onKeyDown={this.doOpenWorkspaceEnter}>
+                    onClick={this.doOpenFolder}
+                    onKeyDown={this.doOpenFolderEnter}>
                     {nls.localizeByDefault('open a folder')}
                 </a>
                 {' ' + nls.localizeByDefault('to start.')}