Fix misconfiguration in travis.yml.

Author: sathielemann

.travis.yml

@@ -12,6 +12,9 @@ matrix:
     - php: 7.0
     - php: 7.1
     - php: 7.2
+    - php: 7.3
+    - php: 7.4
+    - php: nightly
   allow_failures:
     - php: 7.3
     - php: 7.4