Fix pygments import

Closes #12.

Author: lovelydinosaur

snippets/models.py

@@ -2,7 +2,7 @@
 from pygments.lexers import get_all_lexers
 from pygments.styles import get_all_styles
 from pygments.lexers import get_lexer_by_name
-from pygments.formatters import HtmlFormatter
+from pygments.formatters.html import HtmlFormatter
 from pygments import highlight
 
 LEXERS = [item for item in get_all_lexers() if item[1]]