NEW: Add test for PHP 7.3 support (SS4 version)

This also removed the allow_failures nightly build, reasoning that the
PHP 7.3 build is the primary test-case where, and allow_failures builds
are of limited value.

.travis.yml

@@ -23,36 +23,43 @@ matrix:
         - DB=MYSQL
         - PHPCS_TEST=1
         - PHPUNIT_TEST=framework
+
     - php: 7.0
       env:
         - DB=PGSQL
         - PHPUNIT_TEST=framework
+
     - php: 7.1
       if: type IN (cron)
       env:
         - DB=MYSQL
         - PDO=1
         - PHPUNIT_COVERAGE_TEST=framework
+
     - php: 7.2
       env:
         - DB=MYSQL
         - PDO=1
         - PHPUNIT_TEST=framework
-    - php: nightly
+
-      env:
-        - DB=MYSQL
-        - PDO=1
-        - PHPUNIT_TEST=framework
     - php: 7.0
       env:
         - DB=MYSQL
         - PHPUNIT_TEST=cms
-  allow_failures:
+
-    - php: nightly
+    - php: 7.3.0RC1
       env:
         - DB=MYSQL
         - PDO=1
         - PHPUNIT_TEST=framework
+      sudo: required
+      dist: xenial
+      addons:
+        apt:
+          packages:
+            - libzip4
+      services:
+       - mysql
 
 before_script:
 # Extra $PATH
@@ -77,7 +84,6 @@ before_script:
 # Log constants to CI for debugging purposes
   - php ./tests/dump_constants.php
 
-
 script:
   - if [[ $PHPUNIT_TEST ]]; then vendor/bin/phpunit --testsuite $PHPUNIT_TEST; fi
   - if [[ $PHPUNIT_COVERAGE_TEST ]]; then phpdbg -qrr vendor/bin/phpunit --testsuite $PHPUNIT_COVERAGE_TEST --coverage-clover=coverage.xml; fi