chore(composer): Drop PHP 5 support (#3047617)

.travis.yml

-# For PHP 5.5 and lower testing we need to stick to Ubuntu 14.04.
-dist: trusty
 language: php
 sudo: false
 
@@ -9,16 +7,19 @@ cache:
     - $HOME/.composer/cache
     - vendor
 
-matrix:
+jobs:
   fast_finish: true
   include:
-    - php: 5.5
-    - php: 5.6
     - php: 7.0
+      dist: xenial
     - php: 7.1
+      dist: bionic
     - php: 7.2
+      dist: bionic
     - php: 7.3
+      dist: bionic
     - php: 7.4
+      dist: bionic
 
 before_install:
   # Speed up build time by disabling Xdebug when its not needed.

composer.json

@@ -14,7 +14,7 @@
     ],
     "license": "GPL-2.0+",
     "require": {
-        "php": ">=5.5.9",
+        "php": ">=7.0.8",
         "ext-mbstring": "*",
         "squizlabs/php_codesniffer": "^3.4.1",
         "symfony/yaml": ">=2.0.5"
@@ -26,6 +26,6 @@
         }
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.0 || ^5.0 || ^6.0 || ^7.0"
+        "phpunit/phpunit": "^6.0 || ^7.0"
     }
 }