Composer: fix replace directive

I have a feeling that the `replace` directive I put in is not correct.

The information about it in the Composer documentation is a bit sparse, but let's see if this works better.

Ref: https://getcomposer.org/doc/04-schema.md#replace

composer.json

@@ -44,7 +44,7 @@
         "phpunit/phpunit": "^4.0 || ^5.0 || ^6.0 || ^7.0"
     },
     "replace": {
-        "squizlabs/php_codesniffer": "> 2.0"
+        "squizlabs/php_codesniffer": "3.7.2"
     },
     "bin": [
         "bin/phpcs",