Remove Lunr index-building, and update dependencies

* Remove the `--lunr` option from the build command. #87.
* Update PHP dependencies (couldn't be done without removing Lunr as the `markfullmer/porter2` package, on which that depends, has been deleted).

composer.json

@@ -8,7 +8,6 @@
         "ext-sqlite3": "*",
         "addwiki/mediawiki-api-base": "^2.7",
         "endroid/qr-code": "^4.1",
-        "getdkan/lunr.php": "^1.0",
         "league/flysystem": "^1.0",
         "myclabs/php-enum": "^1.5",
         "psr/simple-cache": "^1.0",