Merge pull request #159 from wp-cli/use-latest-php-7-2

Switch PHP 7.2 test to use `WP_VERSION=latest`

Author: gitlost

.travis.yml

@@ -25,7 +25,7 @@ env:
 matrix:
   include:
     - php: 7.2
-      env: WP_VERSION=nightly
+      env: WP_VERSION=latest
     - php: 7.1
       env: WP_VERSION=latest
     - php: 7.0