Upgrade phpcs to ^3.7.1

Author: westonruter

composer.json

@@ -10,11 +10,11 @@
 		"issues": "https://core.trac.wordpress.org/"
 	},
 	"require": {
-		"php": ">=5.6"
+		"php": ">=5.6",
+		"squizlabs/php_codesniffer": "^3.7.1"
 	},
 	"require-dev": {
 		"dealerdirect/phpcodesniffer-composer-installer": "^0.7.0",
-		"squizlabs/php_codesniffer": "3.6.0",
 		"wp-coding-standards/wpcs": "~2.3.0",
 		"phpcompatibility/phpcompatibility-wp": "~2.1.3",
 		"yoast/phpunit-polyfills": "^1.0.1"