ST3 compatibility of ScratchView

When I was trying the "getting start" example in ST3 , I kept encountering error

```
======================================================================
FAIL: test_left_delete_single (a_test.TestLeft)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/vagrant/sublime_plugin_tests/framework.py", line 45, in wrapped_fn
    self.assertTrue(success, failure_reason)
AssertionError: Traceback (most recent call last):
  File "/home/vagrant/.config/sublime-text-3/Packages/sublime-harness-tmp/plugin.py", line 48, in run
    plugin_dict['run']()
KeyError: 'run'
```

I spent quite some time to realize the problem is related to the `import` statement.