Test skipped on Linux

The [`test_complete`](https://github.com/ipython/ipykernel/blob/ff122dd62388af07354cc209387dfa271294e8ee/ipykernel/tests/test_kernel.py#L259) function was failing on Travis in master with:

```python
def test_complete():

with kernel() as kc:

execute(u'a = 1', kc=kc)

wait_for_idle(kc)

cell = 'import IPython\nb = a.'

kc.complete(cell)

> reply = kc.get_shell_msg(block=True, timeout=TIMEOUT)

ipykernel/tests/test_kernel.py:265:

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

../../../virtualenv/python3.6.7/lib/python3.6/site-packages/jupyter_client/client.py:78: in get_shell_msg

return self.shell_channel.get_msg(*args, **kwargs)

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self =

block = True, timeout = 15000

def get_msg(self, block=True, timeout=None):

""" Gets a message if there is one that is ready. """

if block:

if timeout is not None:

timeout *= 1000 # seconds to ms

ready = self.socket.poll(timeout)

else:

ready = self.socket.poll(timeout=0)

if ready:

return self._recv()

else:

> raise Empty

E queue.Empty

../../../virtualenv/python3.6.7/lib/python3.6/site-packages/jupyter_client/blocking/channels.py:57: Empty
----------------------------- Captured stdout call -----------------------------

[IPKernelApp] ERROR | Exception in message handler:

Traceback (most recent call last):

File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/ipykernel/kernelbase.py", line 268, in dispatch_shell

yield gen.maybe_future(handler(stream, idents, msg))

File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/tornado/gen.py", line 735, in run

value = future.result()

File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/tornado/gen.py", line 209, in wrapper

yielded = next(result)

File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/ipykernel/kernelbase.py", line 583, in complete_request

matches = yield gen.maybe_future(self.do_complete(code, cursor_pos))

File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/ipykernel/ipkernel.py", line 354, in do_complete

return self._experimental_do_complete(code, cursor_pos)

File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/ipykernel/ipkernel.py", line 379, in _experimental_do_complete

completions = list(_rectify_completions(code, raw_completions))

File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/IPython/core/completer.py", line 484, in rectify_completions

completions = list(completions)

File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/IPython/core/completer.py", line 1820, in completions

for c in self._completions(text, offset, _timeout=self.jedi_compute_type_timeout/1000):

File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/IPython/core/completer.py", line 1877, in _completions

signature = _make_signature(jm)

File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/IPython/core/completer.py", line 991, in _make_signature

return '(%s)'% ', '.join([f for f in (_formatparamchildren(p) for signature in completion.get_signatures()

File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/IPython/core/completer.py", line 991, in

return '(%s)'% ', '.join([f for f in (_formatparamchildren(p) for signature in completion.get_signatures()

File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/IPython/core/completer.py", line 992, in

for p in signature.defined_names()) if f])

File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/IPython/core/completer.py", line 969, in _formatparamchildren

'Expected "param ...", found %r".' % description)

ValueError: Jedi function parameter description have change format.Expected "param ...", found 'def __sizeof__'".
```

We are skipping the test on Linux in #500 because we couldn't find a way to fix the test.