chore: publish 6.x under 6x tag

Author: vkarpov15

package.json

@@ -105,7 +105,7 @@
     "prepublishOnly": "npm run build-browser",
     "release": "git pull && git push origin master --tags && npm publish",
     "release-5x": "git pull origin 5.x && git push origin 5.x && git push origin 5.x --tags && npm publish --tag 5x",
-    "release-6x": "git pull origin 6.x && git push origin 6.x && git push origin 6.x --tags && npm publish --tag legacy",
+    "release-6x": "git pull origin 6.x && git push origin 6.x && git push origin 6.x --tags && npm publish --tag 6x",
     "mongo": "node ./tools/repl.js",
     "test": "mocha --exit ./test/*.test.js",
     "test-deno": "deno run --allow-env --allow-read --allow-net --allow-run --allow-sys --allow-write ./test/deno.js",