Add missing opening parenthesis

Accidentally removed in 153ec402094adbea673e914385b87f1d99191d0b.
diff --git a/Lib/fontTools/afmLib.py b/Lib/fontTools/afmLib.py
index fea320d..2104b9e 100644
--- a/Lib/fontTools/afmLib.py
+++ b/Lib/fontTools/afmLib.py
@@ -191,7 +191,7 @@
 	def write(self, path, sep='\r'):
 		import time
 		lines = [	"StartFontMetrics 2.0",
-				"Comment Generated by afmLib; at %s" % 
+				"Comment Generated by afmLib; at %s" % (
 						time.strftime("%m/%d/%Y %H:%M:%S", 
 						time.localtime(time.time())))]