Update PHP versions in Travis during merge from 1, removes PHP 7.1 from SS5 builds

.travis.yml

@@ -14,12 +14,13 @@ env:
 matrix:
   fast_finish: true
   include:
-    - php: 7.1
+    - php: 7.2
       env: DB=MYSQL PHPUNIT_TEST=1 PHPCS_TEST=1
-    - php: 7.1
+    - php: 7.3
       env: DB=PGSQL PHPUNIT_TEST=1
-    - php: 7.1
-      env: DB=MYSQL PDO=1 PHPUNIT_COVERAGE_TEST=1
+    - php: 7.3
+      env: DB=MYSQL PHPUNIT_TEST=1
+    - php: 7.3
 
 before_script:
 # Init PHP