Update .travis.yml

Author: geggleto

.travis.yml

@@ -1,8 +1,14 @@
 language: php
 
-php:
-  - 7.1
-  - 7.2
+matrix:
+  include:
+  - php: 7.1
+    env: ANALYSIS='true'
+  - php: 7.2
+  - php: 7.3
+  - php: nightly
+  allow_failures:
+  - php: nightly
 
 before_script: composer install