Use more standard __version__ rather than PILLOW_VERSION (#257)

tests/test_main.py

@@ -1012,7 +1012,7 @@ def test_rotate_deskew_timeout(resources, outdir):
 
 
 @pytest.mark.skipif(
-    PIL.PILLOW_VERSION < '5.0.0',
+    PIL.__version__ < '5.0.0',
     reason="Pillow < 5.0.0 doesn't raise the exception")
 def test_decompression_bomb(resources, outpdf):
     p, out, err = run_ocrmypdf(
@@ -1085,4 +1085,4 @@ def test_skip_repair(spoof_tesseract_noop, resources, outpdf):
         outpdf,
         '--skip-repair',
         env=spoof_tesseract_noop
-    )
+    )