Updated PHP_CodeSniffer requirement

Apparently, if a project relies on a newer version of PHP_CodeSniffer, Diff Sniffer may not work since it will use its own bundled version. Therefore, I have to keep the bundled version up to date.

Author: morozov

composer.json

@@ -11,7 +11,7 @@
   "require": {
     "jean85/pretty-package-versions": "^1.0.3",
     "morozov/bootstrap": "^1.1",
-    "squizlabs/php_codesniffer": "^3.1",
+    "squizlabs/php_codesniffer": "^3.3",
     "php": "^7.1"
   },
   "require-dev": {