⬆️ Support sharedb@6

The only breaking change was dropping Node.js v20 from the test matrix.

Author: alecgibson

package.json

@@ -20,7 +20,7 @@
   },
   "dependencies": {
     "pg": "^8.12.0",
-    "sharedb": "^1.6.0 || ^2.0.0 || ^3.0.0 || ^4.0.0 || ^5.0.0"
+    "sharedb": "^1.6.0 || ^2.0.0 || ^3.0.0 || ^4.0.0 || ^5.0.0 || ^6.0.0"
   },
   "devDependencies": {
     "chai": "^4.4.1",