Fix spelling in documentation (facebookresearch#935)

Summary: Pull Request resolved: facebookresearch#935

Differential Revision: D20077057

Pulled By: ppwwyyxx

fbshipit-source-id: b2d0b0b36b812e162632302bfaa43da535a29fdd

docs/modules/modeling.rst

@@ -7,7 +7,7 @@ detectron2.modeling package
     :show-inheritance:
 
 
-detectron2.modeilng.poolers module
+detectron2.modeling.poolers module
 ---------------------------------------
 
 .. automodule:: detectron2.modeling.poolers
@@ -16,7 +16,7 @@ detectron2.modeilng.poolers module
     :show-inheritance:
 
 
-detectron2.modeilng.sampling module
+detectron2.modeling.sampling module
 ------------------------------------
 
 .. automodule:: detectron2.modeling.sampling
@@ -25,7 +25,7 @@ detectron2.modeilng.sampling module
     :show-inheritance:
 
 
-detectron2.modeilng.box_regression module
+detectron2.modeling.box_regression module
 ------------------------------------------
 
 .. automodule:: detectron2.modeling.box_regression