Some improvements (#846)

* #833: do not require sudo on TravisCI

* #N/A: Add Python dev releases to TravisCI pipeline

Inspired by Brett Cannon's advise [1].

    1: https://snarky.ca/how-to-use-your-project-travis-to-help-test-python-itself/

* #837: try and kill proc and its children

* #N/A: show shell information on `thefuck --version`

* #N/A: omit default arguments to get_close_matches

* #842: add settings var to control number of close matches

* #N/A: remove `n` from the list of `get_closest`'s args

tests/test_utils.py

@@ -2,11 +2,11 @@
 
 import pytest
 import warnings
-from mock import Mock
+from mock import Mock, patch
 from thefuck.utils import default_settings, \
     memoize, get_closest, get_all_executables, replace_argument, \
     get_all_matched_commands, is_app, for_app, cache, \
-    get_valid_history_without_current, _cache
+    get_valid_history_without_current, _cache, get_close_matches
 from thefuck.types import Command
 
 
@@ -50,6 +50,18 @@ class TestGetClosest(object):
                            fallback_to_first=False) is None
 
 
+class TestGetCloseMatches(object):
+    @patch('thefuck.utils.difflib_get_close_matches')
+    def test_call_with_n(self, difflib_mock):
+        get_close_matches('', [], 1)
+        assert difflib_mock.call_args[0][2] == 1
+
+    @patch('thefuck.utils.difflib_get_close_matches')
+    def test_call_without_n(self, difflib_mock, settings):
+        get_close_matches('', [])
+        assert difflib_mock.call_args[0][2] == settings.get('num_close_matches')
+
+
 @pytest.fixture
 def get_aliases(mocker):
     mocker.patch('thefuck.shells.shell.get_aliases',