Tweaked travis config

Author: GrahamCampbell

.travis.yml

@@ -1,6 +1,6 @@
 language: php
 
-sudo: false
+dist: xenial
 
 php:
     - 5.6
@@ -9,11 +9,6 @@ php:
     - 7.2
     - 7.3
 
-before_install:
-    # turn off XDebug, if present
-    - phpenv config-rm xdebug.ini || return 0
-
-install:
-    - composer install --no-interaction --no-progress
+install: travis_retry composer install --no-interaction --no-progress --no-suggest
 
 script: vendor/bin/phpunit