Remove tuple parameter unpacking for python3

When I install pybrowserid in python3 I get the following in my output:

```
....
byte-compiling build/bdist.linux-x86_64/egg/browserid/crypto/_m2_monkeypatch.py to _m2_monkeypatch.cpython-33.pyc
  File "build/bdist.linux-x86_64/egg/browserid/crypto/_m2_monkeypatch.py", line 92
    def new_key((e, n, d)):
                ^
SyntaxError: invalid syntax
....
```

Unpacking as shown above is no longer supported in python3; see [PEP3113](http://www.python.org/dev/peps/pep-3113/).