PEP8 cleanup: fix deprecated raise syntax

Reviewed-by: James Cameron <quozl@laptop.org>
Acked-by: Simon Schampijer <simon@laptop.org>
CC: Aleksey Lim <alsroot@member.fsf.org>

src/sugar/graphics/style.py

@@ -83,7 +83,7 @@ class Color(object):
         if html_color[0] == '#':
             html_color = html_color[1:]
         if len(html_color) != 6:
-            raise ValueError, "input #%s is not in #RRGGBB format" % html_color
+            raise ValueError('input #%s is not in #RRGGBB format' % html_color)
 
         r, g, b = html_color[:2], html_color[2:4], html_color[4:]
         r, g, b = [int(n, 16) for n in (r, g, b)]