adb: Increment ADB_SERVER_VERSION

It was pointed out that we should have done this when we added the "adb root" command.
And doing this will also force people to pick up the recent Linux USB serial number fix.

Signed-off-by: Mike Lockwood <lockwood@android.com>
diff --git a/adb/adb.h b/adb/adb.h
index b9ed556..95610a7 100644
--- a/adb/adb.h
+++ b/adb/adb.h
@@ -33,7 +33,7 @@
 #define ADB_VERSION_MAJOR 1         // Used for help/version information
 #define ADB_VERSION_MINOR 0         // Used for help/version information
 
-#define ADB_SERVER_VERSION    20    // Increment this when we want to force users to start a new adb server
+#define ADB_SERVER_VERSION    21    // Increment this when we want to force users to start a new adb server
 
 typedef struct amessage amessage;
 typedef struct apacket apacket;