travis: make 9.5 test allowed to fail

Author: kulaginm

.travis.yml

@@ -50,7 +50,7 @@ env:
 jobs:
     allow_failures:
         - if: env(PG_BRANCH) = master
-        - if: env(PG_BRANCH) = 9.5
+        - if: env(PG_BRANCH) = REL9_5_STABLE
 #        - if: env(MODE) IN (archive, backup, delta, locking, merge, replica, retention, restore)
 
 # Only run CI for master branch commits to limit our travis usage