chore: update requires (#28)

### What this PR does?
修改 plugin api 和 requires

```release-note
None
```

Author: guqing

build.gradle

@@ -14,7 +14,7 @@ repositories {
 }
 
 dependencies {
-    implementation platform('run.halo.tools.platform:plugin:2.9.0-SNAPSHOT')
+    implementation platform('run.halo.tools.platform:plugin:2.8.0-SNAPSHOT')
     compileOnly 'run.halo.app:api'
 
     testImplementation 'run.halo.app:api'

src/main/resources/plugin.yaml

@@ -9,7 +9,7 @@ metadata:
 spec:
   enabled: true
   version: 1.0.2
-  requires: ">=2.0.0"
+  requires: ">=2.7.0"
   author:
     name: Halo OSS Team
     website: https://github.com/halo-dev