[simple-scan] Add ADF duplex support for Brother DS-720

[Bartosz <bkosiorek src gnome org>]

commit b17e4bc59f417872e3573d73d3c2656c350f8e11
Author: Bartosz Kosiorek <gang65 poczta onet pl>
Date:   Sat Mar 28 00:24:19 2020 +0100

    Add ADF duplex support for Brother DS-720
    
    Fixes: #157

 src/scanner.vala | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/src/scanner.vala b/src/scanner.vala
index fbcc6c6..461322c 100644
--- a/src/scanner.vala
+++ b/src/scanner.vala
@@ -959,6 +959,7 @@ public class Scanner : Object
                 string[] adf_duplex_sources =
                 {
                     "ADF Duplex",
+                    "Duplex ADF", /* Brother DS-720, #157 */
                     Sane.I18N ("ADF Duplex"),
                     "ADF Duplex - Long-Edge Binding", /* Samsung unified driver. LP: # 892915 */
                     "ADF Duplex - Short-Edge Binding",