fix file name (#1759)

Co-authored-by: Ziyue Jiang <ziyue.jiang@gmail.com>

colossalai/pipeline/__init__.py

 from .pipelinable import PipelinableContext, PipelinableModel
-from .layer_sepc import LayerSpec
+from .layer_spec import LayerSpec
 
 __all__ = ['PipelinableModel', 'PipelinableContext', 'LayerSpec']
\ No newline at end of file

colossalai/pipeline/pipelinable.py

@@ -9,7 +9,7 @@ from colossalai.nn.layer.utils import CheckpointModule
 from colossalai.tensor import ColoParameter
 from colossalai.core import global_context as gpc
 from colossalai.context import ParallelMode
-from .layer_sepc import LayerSpec
+from .layer_spec import LayerSpec
 
 
 class PipelinableContext(InsertPostInitMethodToModuleSubClasses):

docs/colossalai/colossalai.pipeline.layer_sepc.rst

 colossalai.pipeline.layer\_sepc
 ===============================
 
-.. automodule:: colossalai.pipeline.layer_sepc
+.. automodule:: colossalai.pipeline.layer_spec
    :members:

docs/colossalai/colossalai.pipeline.rst

@@ -8,6 +8,6 @@ colossalai.pipeline
 .. toctree::
    :maxdepth: 2
 
-   colossalai.pipeline.layer_sepc
+   colossalai.pipeline.layer_spec
    colossalai.pipeline.pipelinable
    colossalai.pipeline.utils