fix: 修复 abstract 前没有 export 的问题 (#4)

* fix: support exporting abstract classes in bundle

* fix: improve abstract class export regex matching

src/bundle.ts

@@ -113,7 +113,7 @@ export async function bundle(options: BundleOptions) {
       return identifier ? identifier = '' : '}'
     } else {
       if (identifier) line = line.slice(4)
-      return line.replace(/^((class|namespace|interface) .+ \{)$/, (_) => `export ${_}`)
+      return line.replace(/^((abstract|class|namespace|interface) .+ \{)$/, (_) => `export ${_}`)
     }
   }).filter(line => line).join(EOL)