Update the CityFormatter to have the header as an argument.

tests/fmt/test_city_formatter.py

@@ -10,3 +10,21 @@ def test_city_format():
 
     assert '- Chernihiv\n' == city_fmt
 
+def test_format_cities():
+    cities = {'data': [
+        {'name': 'Київ'},
+        {'name': 'Чернігів'}
+    ]}
+
+    expected_format = "".join([
+        "# Міста\n\n",
+        "- Київ\n",
+        "- Чернігів\n",
+    ])
+
+    formatter = CityFormatter()
+
+    cities_fmt = formatter.format_all(cities)
+
+    assert expected_format == cities_fmt
+