improve useDatabase

package.json

 {
   "name": "koishi-plugin-fortune",
-  "version": "2.0.1",
+  "version": "2.1.0",
   "description": "Koishi 的算卦插件",
   "main": "dist/index.js",
   "typings": "dist/src/index.d.ts",
@@ -28,7 +28,7 @@
     "source-map-support": "^0.5.20"
   },
   "peerDependencies": {
-    "koishi": "^4.0.0-alpha.8"
+    "koishi": "^4.0.0-alpha.10"
   },
   "devDependencies": {
     "@stdlib/random-base-mt19937": "^0.0.5",
@@ -39,7 +39,7 @@
     "eslint": "^7.32.0",
     "eslint-config-prettier": "^8.3.0",
     "eslint-plugin-prettier": "^3.4.1",
-    "koishi": "^4.0.0-alpha.8",
+    "koishi": "^4.0.0-alpha.10",
     "moment": "^2.29.1",
     "mustache": "^4.2.0",
     "prettier": "^2.4.1",

src/plugin.ts

@@ -46,8 +46,8 @@ export class MyPlugin {
     return result;
   }
   apply(ctx: Context, config: Config) {
-    ctx.on('connect', () => {
-      if (ctx.database && this.config.useDatabase) this.useDatabase = true;
+    ctx.on('service/database', () => {
+      if (this.config.useDatabase) this.useDatabase = !!ctx.database;
     });
     this.ctx = ctx;
     this.config = Schema.validate(config, this.schema);