Improve exception type.

ImportError isn't really appropriate when there's no import involved.

src/transformers/commands/serving.py

@@ -107,7 +107,7 @@ class ServeCommand(BaseTransformersCLICommand):
         self._host = host
         self._port = port
         if not _serve_dependancies_installed:
-            raise ImportError(
+            raise RuntimeError(
                 "Using serve command requires FastAPI and unicorn. "
                 "Please install transformers with [serving]: pip install transformers[serving]."
                 "Or install FastAPI and unicorn separatly."

src/transformers/commands/train.py

@@ -8,7 +8,7 @@ from transformers.commands import BaseTransformersCLICommand
 
 
 if not is_tf_available() and not is_torch_available():
-    raise ImportError("At least one of PyTorch or TensorFlow 2.0+ should be installed to use CLI training")
+    raise RuntimeError("At least one of PyTorch or TensorFlow 2.0+ should be installed to use CLI training")
 
 # TF training parameters
 USE_XLA = False