[gnome-builder] rustup: fix typo

[Christian Hergert <chergert src gnome org>]

commit a5ac446bf9e80522e44991beefd2c1eb65989c2e
Author: Christian Hergert <chergert redhat com>
Date:   Tue Feb 28 15:27:59 2017 -0800

    rustup: fix typo

 plugins/rustup/rustup_plugin/__init__.py |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/plugins/rustup/rustup_plugin/__init__.py b/plugins/rustup/rustup_plugin/__init__.py
index 80d3c6a..56d9a67 100644
--- a/plugins/rustup/rustup_plugin/__init__.py
+++ b/plugins/rustup/rustup_plugin/__init__.py
@@ -325,7 +325,7 @@ class RustupInstaller(Ide.Transfer):
         try:
             sub_process = launcher.spawn()
         except Exception as ex:
-            task.return_error(GLib.Error(message=repr(ex))
+            task.return_error(GLib.Error(message=repr(ex)))
 
         sub_process.wait_async(cancellable, self._wait_cb, task)