[Security] Bump squizlabs/php_codesniffer from 2.7.0 to 3.4.0

Bumps [squizlabs/php_codesniffer](https://github.com/squizlabs/PHP_CodeSniffer) from 2.7.0 to 3.4.0. **This update includes security fixes.**
- [Release notes](https://github.com/squizlabs/PHP_CodeSniffer/releases)
- [Commits](squizlabs/PHP_CodeSniffer@2.7.0...3.4.0)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot-support

composer.json

@@ -12,7 +12,7 @@
   },
   "require-dev": {
     "phpunit/phpunit": "^5.2.3",
-    "squizlabs/php_codesniffer": "^2.6",
+    "squizlabs/php_codesniffer": "^3.4",
     "phake/phake": "^2.3"
   },
   "autoload": {