Renamed graph_runtime references to graph_executor. (#31)

Following TVM's rename in https://github.com/apache/tvm/pull/7653,
update to avoid errors when tvm.contrib.graph_runtime is removed
entirely.
diff --git a/apps/deploy/python_deploy.py b/apps/deploy/python_deploy.py
index 2502046..4f447bb 100644
--- a/apps/deploy/python_deploy.py
+++ b/apps/deploy/python_deploy.py
@@ -26,7 +26,7 @@
 import numpy as np
 
 import tvm
-from tvm.contrib import graph_runtime, download
+from tvm.contrib import graph_executor, download
 
 
 CTX = tvm.ext_dev(0)
@@ -50,7 +50,7 @@
 
     lib = tvm.runtime.load_module("./build/model/lib.so")
 
-    model = graph_runtime.create(graph, lib, CTX)
+    model = graph_executor.create(graph, lib, CTX)
 
     with open("./build/model/params.params", "rb") as paramfile:
         param_bytes = paramfile.read()