drop php 7.1 and older; add php 8

# Conflicts:
#	.travis.yml

.travis.yml

@@ -16,20 +16,9 @@ script:
 matrix:
   fast_finish: true
   include:
-    - php: 5.3
-      dist: precise
-      services: redis-server
-      before_install: skip
-    - php: 5.4
-      dist: trusty
-    - php: 5.5
-      dist: trusty
-    - php: 5.6
-    - php: 7.0
-    - php: 7.1
     - php: 7.2
     - php: 7.3
     - php: 7.4
-    - php: nightly # PHP 8.0.0-dev
+    - php: 8.0
   allow_failures:
-    - php: nightly
+   - php: 8.0

composer.json

@@ -28,7 +28,7 @@
         }
     ],
     "require": {
-        "php": ">=5.3.9"
+        "php": "^7.2"
     },
     "require-dev": {
         "phpunit/phpunit": "~4.8",