deps: Require PHP 7.1 or later

We already no longer tested for PHP 7.0 or below for more than 4 years.

Author: cmfcmf

composer.json

@@ -17,7 +17,7 @@
         "source": "https://github.com/cmfcmf/OpenWeatherMap-PHP-API.git"
     },
     "require": {
-        "php": ">=7.0.0",
+        "php": ">=7.1.0",
         "ext-json": "*",
         "ext-libxml": "*",
         "ext-simplexml": "*",