fix jump to pdf from command palette

Currently when calling Jump to PDF from the command palette in ST3 it has this error (and nothing happens)

```
Traceback (most recent call last):
  File "C:\Program Files (x86)\Sublime Text 3\sublime_plugin.py", line 549, in run_
    return self.run(edit)
  File "AppData\Roaming\Sublime Text 3\Packages\LaTeXTools\jumpToPDF.py", line 36, in run
    from_keybinding = args["from_keybinding"]
KeyError: 'from_keybinding'
```

This commit fixes that.