keep old Travis Linux distro

hboutemy · web-flow · commit a11146c02e3e · 2019-08-09T19:01:12.000+01:00
newer distro only have JDK 9+ see https://travis-ci.community/t/install-of-oracle-jdk-8-failing/3038/8
diff --git a/.travis.yml b/.travis.yml
@@ -1,4 +1,5 @@
 language: java
+dist: trusty
 jdk:
   - oraclejdk8
   - oraclejdk7
