fix: update outdated error messages in fastapi_proxy_lib.fastapi

Author: WSH032

src/fastapi_proxy_lib/fastapi/__init__.py

@@ -12,8 +12,8 @@
     msg: str = dedent(
         """\
         `fastapi` is not installed.
-        `fastapi_proxy.app` module requires installing `fastapi` first:
-            pip install fastapi-proxy[standard]
+        `fastapi_proxy_lib.fastapi` module requires installing `fastapi` first:
+            pip install fastapi-proxy-lib[standard]
         """
     )
     raise RuntimeError(msg)