Removed old PHP versions from Travis config. Touch #16

.travis.yml

@@ -1,5 +1,5 @@
 sudo: false
-dist: trusty
+dist: xenial
 
 language: php
 
@@ -18,18 +18,14 @@ cache:
 
 matrix:
   include:
-    - php: 7.2
+    - php: 7.4
       env: WP_VERSION=latest
-    - php: 7.1
+    - php: 7.3
       env: WP_VERSION=latest
-    - php: 7.0
+    - php: 7.2
       env: WP_VERSION=latest
-    - php: 5.6
+    - php: 7.2
       env: WP_VERSION=4.0
-    - php: 5.6
-      env: WP_VERSION=latest
-    - php: 5.6
-      env: WP_VERSION=trunk
 
 before_script:
   - export PATH="$HOME/.composer/vendor/bin:$PATH"