Stop parsing language-variable cat output to make cat_dir more reliable. (#827)

* Stop parsing language-variable cat output to make cat_dir more reliable.

* Add missing semicolon in readme

tests/rules/test_cat_dir.py

@@ -3,20 +3,29 @@ from thefuck.rules.cat_dir import match, get_new_command
 from thefuck.types import Command
 
 
+@pytest.fixture
+def isdir(mocker):
+    return mocker.patch('thefuck.rules.cat_dir'
+                        '.os.path.isdir')
+
+
 @pytest.mark.parametrize('command', [
     Command('cat foo', 'cat: foo: Is a directory\n'),
     Command('cat /foo/bar/', 'cat: /foo/bar/: Is a directory\n'),
     Command('cat cat/', 'cat: cat/: Is a directory\n'),
 ])
-def test_match(command):
+def test_match(command, isdir):
+    isdir.return_value = True
     assert match(command)
 
 
 @pytest.mark.parametrize('command', [
     Command('cat foo', 'foo bar baz'),
     Command('cat foo bar', 'foo bar baz'),
+    Command('notcat foo bar', 'some output'),
 ])
-def test_not_match(command):
+def test_not_match(command, isdir):
+    isdir.return_value = False
     assert not match(command)
 
 
@@ -26,4 +35,5 @@ def test_not_match(command):
     (Command('cat cat', 'cat: cat: Is a directory\n'), 'ls cat'),
 ])
 def test_get_new_command(command, new_command):
+    isdir.return_value = True
     assert get_new_command(command) == new_command