patch 8.1.0685: get_buf_tv() is named inconsistently

Problem:    get_buf_tv() is named inconsistently.
Solution:   Rename it to tv_get_buf(). (Yegappan Lakshmanan, closes #3759)
diff --git a/src/version.c b/src/version.c
index 0493ec4..b9fe301 100644
--- a/src/version.c
+++ b/src/version.c
@@ -800,6 +800,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    685,
+/**/
     684,
 /**/
     683,