patch 9.0.0057: has('patch-xxx') returns true

Problem:    has('patch-xxx') returns true.
Solution:   Check for digit. (closes #10751)
diff --git a/src/version.c b/src/version.c
index 87a8d10..ee421e4 100644
--- a/src/version.c
+++ b/src/version.c
@@ -736,6 +736,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    57,
+/**/
     56,
 /**/
     55,