Update docs for new Predictor API

Author: deliahu

docs/deployments/python.md

@@ -39,8 +39,9 @@ In addition to supporting Python models via the Python Predictor interface, Cort
 ```yaml
 - kind: api
   name: my-api
-  python:
-    predictor: predictor.py
+  predictor:
+    type: python
+    path: predictor.py
   compute:
     gpu: 1
 ```

docs/packaging-models/onnx.md

@@ -34,5 +34,5 @@ Reference your model in an `api`:
   predictor:
     type: onnx
     model: s3://my-bucket/model.onnx
-    predictor: predictor.py
+    path: predictor.py
 ```

docs/packaging-models/tensorflow.md

@@ -41,7 +41,7 @@ Reference your model in an `api`:
   predictor:
     type: tensorflow
     model: s3://my-bucket/bert
-    predictor: predictor.py
+    path: predictor.py
 ```
 
 You may also zip the export directory before uploading it:
@@ -60,5 +60,5 @@ Reference the zipped model in an `api`:
   predictor:
     type: tensorflow
     model: s3://my-bucket/bert.zip
-    predictor: predictor.py
+    path: predictor.py
 ```