Adding rule for forgotten '-r' when grepping folders

tests/rules/test_grep_recursive.py

@@ -0,0 +1,12 @@
+from thefuck.rules.grep_recursive import match, get_new_command
+from tests.utils import Command
+
+
+def test_match():
+    assert match(Command('grep blah .', stderr='grep: .: Is a directory'), None)
+    assert not match(Command(), None)
+
+
+def test_get_new_command():
+    assert get_new_command(
+        Command('grep blah .'), None) == 'grep -r blah .'