Drop older test versions.

Maikuolan · Maikuolan · commit eb65f2e6e14a · 2020-03-08T00:21:55.000+08:00
diff --git a/.travis.yml b/.travis.yml
@@ -3,10 +3,8 @@ dist: trusty
 language: php
 
 php:
- - '7.0'
- - '7.1'
- - '7.2'
  - '7.3'
+ - '7.4'
 
 before_script:
  - phpenv config-rm xdebug.ini || true
