bpo-39035: travis: Don't use beta group (GH-17602)

diff --git a/.travis.yml b/.travis.yml
index 807a7b2..b1d50d4 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,6 +1,5 @@
 language: c
 dist: xenial
-group: beta
 
 # To cache doc-building dependencies and C compiler output.
 cache: