Show Pillow version in the tests header

tests/conftest.py

@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 
 import os
+import PIL
 import pytest
 
 from sigal.settings import read_settings
@@ -12,3 +13,7 @@ CURRENT_DIR = os.path.abspath(os.path.dirname(__file__))
 def settings():
     """Read the sample config file."""
     return read_settings(os.path.join(CURRENT_DIR, 'sample', 'sigal.conf.py'))
+
+
+def pytest_report_header(config):
+    return "project deps: Pillow-{}".format(PIL.PILLOW_VERSION)