Typo in ModularServer's last parameter

[yoon-gu]

It should have been placed in the form of dictionary.

class ModularServer(tornado.web.Application):
    ...
    def __init__(self, model_cls, visualization_elements, name="Mesa Model",
                 model_params={}):

[coveralls]

Coverage remained the same at 77.062% when pulling e7c1f4d on yoon-gu:master into 00e88d2 on projectmesa:master.

[Corvince]

Thanks for the PR! Looks good and fixes #717