docs: update install command

kxxt · kxxt · commit 5ec409d90062 · 2022-05-02T10:12:48.000+08:00
diff --git a/README.md b/README.md
@@ -23,7 +23,7 @@ You can try the Azure TTS API online: https://azure.microsoft.com/en-us/services
 ## Installation
 
 ```sh
-$ pip install aspeak
+$ pip install --upgrade aspeak
 ```
 
 ## Usage
