travis: fix broken build due to incomplete python install

Unsure of the root cause. See this build log:
 https://travis-ci.org/vincentbernat/lldpd/jobs/275129851

diff --git a/.travis.yml b/.travis.yml
index 1ba6ca11cba4df116fe67a312e28a30cfd2114f4..4676d08c452711b7bc191e0e2df7bca541e0356b 100644 (file)
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,4 +1,5 @@
 language: c
+group: deprecated-2017Q3
 os: linux
 dist: trusty
 compiler: gcc