Upgraded travis dist to repair broken php8 tests

Author: Geolim4

.travis.yml

@@ -9,7 +9,7 @@
 # @author Georges.L (Geolim4)  <contact@geolim4.com>
 #
 os: linux
-dist: trusty
+dist: bionic
 language: php
 services:
   - memcached
@@ -32,25 +32,16 @@ before_script:
   - mongo pfc_test --eval 'db.createUser({user:"travis",pwd:"test",roles:["readWrite"]});'
 
 php:
-  # - 5.3
-  # - 5.4
-  # - 5.5
-  # - 5.6
-  #- 7.0
-  # - 7.1
-  # - 7.2
   - 7.3
   - 7.4
   - 8.0
-  # - nightly # crashes on almost every builds, very unstable
   - hhvm
 
 jobs:
   fast_finish: true
   allow_failures:
     # - php: nightly
     - php: hhvm
-    - php: 8.0
 
 install:
   - ./bin/ci/install_dependencies.sh