drop support for PHP < 7.1

Author: xabbuh

.github/workflows/unit-tests.yaml

@@ -9,11 +9,6 @@ jobs:
         strategy:
             matrix:
                 php:
-                    - '5.3'
-                    - '5.4'
-                    - '5.5'
-                    - '5.6'
-                    - '7.0'
                     - '7.1'
                     - '7.2'
                     - '7.3'

composer.json

@@ -13,11 +13,11 @@
         }
     ],
     "require": {
-        "php": ">=5.3.0",
+        "php": ">=7.1",
         "ext-mbstring": "*"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.8|^5.7|^6.5|^7.5|^8.5|^9.6"
+        "phpunit/phpunit": "^7.5|^8.5|^9.6"
     },
     "autoload": {
         "psr-0": {"Parsedown": ""}