Modify minimum php requirement in composer.json, a=chris

diff --git a/composer.json b/composer.json
index e47cc015a..6af290893 100644
--- a/composer.json
+++ b/composer.json
@@ -11,7 +11,7 @@
     ],
     "minimum-stability": "stable",
     "require": {
-        "php": ">=7.1.0",
+        "php": ">=7.4.0",
         "ext-dom": "*",
         "ext-gd": "*",
         "ext-json": "*",