preprocess_cssless.diff

diff --git a/commands/preprocess_cssless.py b/commands/preprocess_cssless.py
index 11170e3..0c29d96 100644
--- a/commands/preprocess_cssless.py
+++ b/commands/preprocess_cssless.py
@@ -25,8 +25,11 @@ import warnings
 import cssutils
 from lxml import etree
 from lxml.etree import strip_elements
+import premailer
 from premailer import Premailer
 
+premailer_version = premailer.__version__.split('.')
+premailer_is_new=len(premailer_version) >= 2 and int(premailer_version[0]) >= 3 and int(premailer_version[1]) >= 9
 
 def preprocess_html_merge_cssless(src_path, dst_path):
     with open(src_path, 'r', encoding='utf-8') as a_file:
@@ -72,8 +75,13 @@ def preprocess_html_merge_css(root, src_path):
 
     with warnings.catch_warnings():
         warnings.simplefilter("ignore")
-        premailer = Premailer(root, base_url=src_path,
-                              disable_link_rewrites=True, remove_classes=True)
+        if premailer_is_new:
+            premailer = Premailer(root, base_url=src_path,
+                                  disable_link_rewrites=True, remove_classes=True,
+                                  allow_loading_external_files=True)
+        else:
+            premailer = Premailer(root, base_url=src_path,
+                                  disable_link_rewrites=True, remove_classes=True)
         root = premailer.transform().getroot()
 
     return output.getvalue()