patch 8.1.0313: information about a swap file is unavailable

Problem:    Information about a swap file is unavailable.
Solution:   Add swapinfo(). (Enzo Ferber)
diff --git a/src/version.c b/src/version.c
index d752d04..d0052fa 100644
--- a/src/version.c
+++ b/src/version.c
@@ -795,6 +795,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    313,
+/**/
     312,
 /**/
     311,