Change syntax of "next" in get_commonality_of_user for py2neo v4

[seanofahey]

First thanks for the code and tutorial -- they are both very helpful.

Issue:

• When logged in as a user and looking at the profile page of another user, the system does not correctly display the number of likes or the common tags.

Potential Cause:

• the return call on the get_commonality_of_user method in models.py uses the following syntax:

return graph.run(query, they=other.username, you=self.username).next

Fix:
Modify the return call to be:
return graph.run(query, they=other.username, you=self.username).next()

or wrap it with:
return next(graph.run(query, they=other.username, you=self.username))