Update dependencies and address change in sniff names and load mf2 parser only within scope

Author: dshanske

.gitignore

@@ -13,3 +13,4 @@ wordpress
 !/vendor/p3k/emoji-detector/LICENSE
 .DS_Store
 package-lock.json
+composer.lock

composer.json

@@ -15,15 +15,16 @@
   "require": {
     "php": ">=5.3.0",
     "composer/installers": "~1.0",
-    "mf2/mf2": "^0.4.3",
-    "p3k/emoji-detector": "^0.2.0"
+    "mf2/mf2": "*",
+    "p3k/emoji-detector": "*"
   },
   "require-dev": {
     "phpunit/phpunit": "5.7.*",
     "squizlabs/php_codesniffer": "^2.2 || ^3.0.2",
-    "wimg/php-compatibility": "*",
     "wp-coding-standards/wpcs": "*",
-    "dealerdirect/phpcodesniffer-composer-installer": "^0.4.3"
+    "dealerdirect/phpcodesniffer-composer-installer": "^0.4.3",
+    "phpcompatibility/php-compatibility": "^9.0",
+    "phpcompatibility/phpcompatibility-wp": "^2.0"
   },
   "scripts": {
     "install-codestandards": [