Update Docker image version in installation steps (#175)

Author: her001

README.md

@@ -94,7 +94,7 @@ Releases are available
 ### 🐳 From Docker Image
 
 ```shell
-docker run -e LIVEKIT_URL="ws://somewhere" -e LIVEKIT_KEY=devkey -e LIVEKIT_SECRET=secret -e LIVEKIT_FULL_ACCESS_HOMESERVERS=example.com -p 8080:8080 ghcr.io/element-hq/lk-jwt-service:0.3.0
+docker run -e LIVEKIT_URL="ws://somewhere" -e LIVEKIT_KEY=devkey -e LIVEKIT_SECRET=secret -e LIVEKIT_FULL_ACCESS_HOMESERVERS=example.com -p 8080:8080 ghcr.io/element-hq/lk-jwt-service:latest
 ```
 
 ### 📦 From Release