Update humanmade/meta-tags requirement from ^0.1.6 to ^0.1.8

Updates the requirements on [humanmade/meta-tags](https://github.com/humanmade/meta-tags) to permit the latest version.
- [Release notes](https://github.com/humanmade/meta-tags/releases)
- [Commits](humanmade/meta-tags@0.1.6...0.1.8)

---
updated-dependencies:
- dependency-name: humanmade/meta-tags
  dependency-type: direct:production
...

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

composer.json

@@ -13,7 +13,7 @@
         "php": ">=7.1",
         "humanmade/wp-seo": "0.14.0",
         "humanmade/hm-redirects": "~0.5.2",
-        "humanmade/meta-tags": "^0.1.6"
+        "humanmade/meta-tags": "^0.1.8"
     },
     "autoload": {
         "files": [