patch 8.1.0557: Termdebug: gdb may use X.Y for breakpoint number

Problem:    Termdebug: gdb may use X.Y for breakpoint number.
Solution:   Handle X.Y breakpoint numbers. (Yasuhiro Matsumoto, close #3641)
diff --git a/src/version.c b/src/version.c
index 55a9af6..bdc8007 100644
--- a/src/version.c
+++ b/src/version.c
@@ -793,6 +793,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    557,
+/**/
     556,
 /**/
     555,