Add PHP 7.3 to Travis builds and use recipe-cms instead of recipe-core

Fixes the version incompatibility with silverstripe/versioned and its new interfaces

.travis.yml

@@ -1,9 +1,5 @@
 language: php
 
-env:
-  global:
-    - COMPOSER_ROOT_VERSION="3.1.x-dev"
-
 matrix:
   include:
     - php: 5.6
@@ -14,15 +10,15 @@ matrix:
       env: DB=PGSQL RECIPE_VERSION=4.2.x-dev PHPUNIT_COVERAGE_TEST=1
     - php: 7.2
       env: DB=MYSQL RECIPE_VERSION=4.3.x-dev PHPUNIT_TEST=1
-    - php: 7.2
+    - php: 7.3
       env: DB=MYSQL RECIPE_VERSION=4.x-dev PHPUNIT_TEST=1
 
 before_script:
   - phpenv rehash
   - phpenv config-rm xdebug.ini
 
   - composer validate
-  - composer require silverstripe/recipe-core "$RECIPE_VERSION"  --no-update
+  - composer require silverstripe/recipe-cms:"$RECIPE_VERSION"  --no-update
   - if [[ $DB == PGSQL ]]; then composer require silverstripe/postgresql:2.1.x-dev --no-update; fi
   - composer install --prefer-dist --no-interaction --no-progress --no-suggest --optimize-autoloader --verbose --profile