Add jinja2 2.6 dependency

[Christian S. Perone]

Using jinja2 2.5 version causes the following traceback (reported by Liquid_Fire on Reddit):

Traceback (most recent call last):
  File "C:\Python27\lib\site-packages\flask\app.py", line 1518, in __call__
    return self.wsgi_app(environ, start_response)
  File "C:\Python27\lib\site-packages\flask\app.py", line 1506, in wsgi_app
    response = self.make_response(self.handle_exception(e))
  File "C:\Python27\lib\site-packages\flask\app.py", line 1504, in wsgi_app
    response = self.full_dispatch_request()
  File "C:\Python27\lib\site-packages\flask\app.py", line 1264, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "C:\Python27\lib\site-packages\flask\app.py", line 1262, in full_dispatch_request
    rv = self.dispatch_request()
  File "C:\Python27\lib\site-packages\flask\app.py", line 1248, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "C:\Python27\lib\site-packages\stallion\main.py", line 118, in index
    return render_template('system_information.html', **data)
  File "C:\Python27\lib\site-packages\flask\templating.py", line 123, in render_template
    context, ctx.app)
  File "C:\Python27\lib\site-packages\flask\templating.py", line 107, in _render
    rv = template.render(context)
  File "C:\Python27\lib\site-packages\jinja2-2.5.5-py2.7.egg\jinja2\environment.py", line 891, in render
    return self.environment.handle_exception(exc_info, True)
  File "C:\Python27\lib\site-packages\stallion\templates\system_information.html", line 1, in top-level template code
    {% extends "main.html" %}
  File "C:\Python27\lib\site-packages\stallion\templates\main.html", line 33, in top-level template code
    {% for dist in distributions|sort(attribute="project_name") %}
TypeError: do_sort() got an unexpected keyword argument 'attribute'