Add PHP 7.3 to Travis builds

.travis.yml

@@ -1,24 +1,21 @@
 # See https://github.com/silverstripe/silverstripe-travis-support for setup details
 
-sudo: false
+dist: trusty
 
 language: php
 
-php:
-  - 5.4
-  - 5.5
-
-env:
-  - DB=MYSQL CORE_RELEASE=3.5
-
 matrix:
   include:
-    - php: 5.6
-      env: DB=MYSQL CORE_RELEASE=3
-    - php: 5.6
-      env: DB=PGSQL CORE_RELEASE=3.4
-    - php: 7.1
+    - php: '5.6'
       env: DB=MYSQL CORE_RELEASE=3.6
+    - php: '7.0'
+      env: DB=PGSQL CORE_RELEASE=3.7
+    - php: '7.1'
+      env: DB=MYSQL CORE_RELEASE=3.7
+    - php: '7.2'
+      env: DB=MYSQL CORE_RELEASE=3.7
+    - php: '7.3'
+      env: DB=MYSQL CORE_RELEASE=3.7
 
 before_script:
   - composer self-update || true

composer.json

@@ -14,7 +14,7 @@
 		"silverstripe/cms": "^3.2"
 	},
 	"require-dev": {
-		"phpunit/PHPUnit": "~3.7@stable"
+		"phpunit/phpunit": "^5.7"
 	},
 	"extra": {
 		"branch-alias": {