Upgrade dependencies (#4)

* Promise v1

* Badges

* Documentation

* Upgrade to phpgt/promise v2

* Backwards compatibility with PHP 7.4

Author: Greg Bowler

composer.json

@@ -4,8 +4,9 @@
 	"license": "MIT",
 
 	"require": {
-		"php": ">=8.0",
-		"phpgt/promise": "^1.0"
+		"php": ">=7.4",
+		"ext-dom": "*",
+		"phpgt/promise": "^2.0"
 	},
 	"require-dev": {
 		"phpunit/phpunit": "9.*",