Update johnbillion/query-monitor requirement from ^3.14.1 to ^3.15.0

Updates the requirements on [johnbillion/query-monitor](https://github.com/johnbillion/query-monitor) to permit the latest version.
- [Release notes](https://github.com/johnbillion/query-monitor/releases)
- [Commits](johnbillion/query-monitor@3.14.1...3.15.0)

---
updated-dependencies:
- dependency-name: johnbillion/query-monitor
  dependency-type: direct:production
...

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

composer.json

@@ -17,7 +17,7 @@
 		]
 	},
 	"require": {
-		"johnbillion/query-monitor": "^3.14.1",
+		"johnbillion/query-monitor": "^3.15.0",
 		"altis/dev-tools-command": "^0.7.2",
 		"wp-phpunit/wp-phpunit": "6.2.2",
 		"yoast/phpunit-polyfills": "^1.0.5",