Fix imports of token types for Django 2.1

Author: tsouvarev

django_babel/extract.py

@@ -1,5 +1,20 @@
 # -*- coding: utf-8 -*-
-from django.template.base import Lexer, TOKEN_TEXT, TOKEN_VAR, TOKEN_BLOCK
+try:
+    from django.template.base import Lexer, TOKEN_TEXT, TOKEN_VAR, TOKEN_BLOCK
+except ImportError:
+    try:
+        # Django 1.8 moved most stuff to .base
+        from django.template.base import (
+            Lexer, TOKEN_TEXT, TOKEN_VAR, TOKEN_BLOCK,
+        )
+    except ImportError:
+        # Django 2.1+
+        from django.template.base import Lexer, TokenType
+
+        TOKEN_TEXT = TokenType.TEXT
+        TOKEN_VAR = TokenType.VAR
+        TOKEN_BLOCK = TokenType.BLOCK
+
 from django.utils.translation import trim_whitespace
 from django.utils.encoding import smart_text