Sort line numbers of duplicates

The logic of `get_occurrence_in_object()` previously assumed the input
line numbers were sorted.

This fixes #29.

autoflake.py

@@ -540,7 +540,7 @@ def get_occurrence_in_object(line, line_number, key, marked_line_numbers,
            closing_object_lines[i] >= line_number][0]
 
     obj_lines = []
-    for ln in marked_line_numbers:
+    for ln in sorted(marked_line_numbers):
         if (
             opening_object_lines[obj] <= ln and
             closing_object_lines[obj] >= ln and

test_autoflake.py

@@ -432,6 +432,30 @@ def test_filter_code_with_duplicate_key(self):
   (0,1): 3,
 }
 print(a)
+""", remove_duplicate_keys=True)))
+
+    def test_filter_code_with_duplicate_key_longer(self):
+        self.assertEqual(
+            """\
+{
+    'a': 0,
+    'c': 2,
+    'd': 3,
+    'e': 4,
+    'f': 5,
+    'b': 6,
+}
+""",
+            ''.join(autoflake.filter_code("""\
+{
+    'a': 0,
+    'b': 1,
+    'c': 2,
+    'd': 3,
+    'e': 4,
+    'f': 5,
+    'b': 6,
+}
 """, remove_duplicate_keys=True)))
 
     def test_filter_code_with_special_re_symbols_in_key(self):