Bump wyrihaximus/constants from 1.5.0 to 1.6.0

Bumps [wyrihaximus/constants](https://github.com/WyriHaximus/php-constants) from 1.5.0 to 1.6.0.
- [Release notes](https://github.com/WyriHaximus/php-constants/releases)
- [Commits](WyriHaximus/php-constants@1.5.0...1.6.0)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

composer.json

@@ -15,7 +15,7 @@
         "react/event-loop": "^1.1",
         "react/promise": "^2.7",
         "reactivex/rxphp": "^2.0",
-        "wyrihaximus/constants": "^1.4.3",
+        "wyrihaximus/constants": "^1.6.0",
         "wyrihaximus/metrics": "^1.0"
     },
     "require-dev": {