fix(plantuml): correct cache

src/main/server/plantuml.ts

@@ -99,7 +99,7 @@ export default async function (data: string): Promise<{ content: any, type: stri
   } else {
     const url = api.replace('{data}', plantumlBase64(data))
     const dispatcher = await getAction('get-proxy-dispatcher')(url)
-    let type = ''
+    let type = api.includes('/svg/') ? 'image/svg+xml' : 'image/png'
 
     const cacheKey = getCacheKey(api, type, data)
     const content = await getCacheData(cacheKey, async () => {