Update unstable library feature list by Travis CI build 1538

Author: Travis CI

unstable_library_feature.txt

@@ -203,3 +203,4 @@ vecdeque_binary_search              78021    2020-10-16 18:17:55 +0200  2020-10-
 pin_static_ref                      78186    2020-10-21 16:30:41 +0200  2020-10-21 16:30:41 +0200
 option_insert                       78271    2020-10-23 11:44:58 +0200  2020-10-23 11:44:58 +0200
 panic_any                           78500    2020-10-28 21:23:45 +0100  2020-10-28 21:23:45 +0100
+atomic_fetch_update                 78639    2020-11-01 13:24:22 -0500  2020-11-01 13:24:22 -0500