Don't include ASC in primary key script

ASC is the default so it isn't necessary to specify it.
Doing so causes unwanted diffs for people who use SchemaZen for db
version control.

model/ConstraintColumn.cs

@@ -11,7 +11,7 @@ public ConstraintColumn(string columnName, bool desc) {
         }
 
         public string Script() {
-            return "[" + ColumnName + "]" + (Desc ? " DESC" : " ASC");
+            return "[" + ColumnName + "]" + (Desc ? " DESC" : "");
         }
     }
 }