Add PHP 7.4 (snapshot) to Travis CI matrix.

Author: jmalloc

.travis.yml

@@ -4,11 +4,13 @@ php:
 - '7.1'
 - '7.2'
 - '7.3'
-- nightly
+- '7.4snapshot'
+- 'nightly'
 matrix:
   fast_finish: true
   allow_failures:
-  - php: nightly
+  - php: '7.4snapshot'
+  - php: 'nightly'
 before_install:
 - phpenv config-rm xdebug.ini || true
 - "[[ $GITHUB_TOKEN ]] && composer config --global github-oauth.github.com $GITHUB_TOKEN"