[Minor] Fix percent sign in statistics learning condition

conf/statistic.conf

@@ -57,10 +57,10 @@ return function(task, is_spam, is_unlearn)
     end
 
     if is_unlearn and (not in_class) then
-      return false,string.format('not in class %s; probability %.2f%%',
+      return false,string.format('not in class %s; probability %.2f%%%%',
         cl, math.abs((prob - 0.5) * 200.0))
     elseif (not is_unlearn) and in_class then
-      return false,string.format('already in class %s; probability %.2f%%',
+      return false,string.format('already in class %s; probability %.2f%%%%',
         cl, math.abs((prob - 0.5) * 200.0))
     end
   end