Fix dependency error message in ServeCommand (#16033)

"uvicorn" is misspelled as "unicorn".

src/transformers/commands/serving.py

@@ -131,9 +131,9 @@ class ServeCommand(BaseTransformersCLICommand):
 
         if not _serve_dependencies_installed:
             raise RuntimeError(
-                "Using serve command requires FastAPI and unicorn. "
+                "Using serve command requires FastAPI and uvicorn. "
                 'Please install transformers with [serving]: pip install "transformers[serving]".'
-                "Or install FastAPI and unicorn separately."
+                "Or install FastAPI and uvicorn separately."
             )
         else:
             logger.info(f"Serving model over {host}:{port}")