Revert "update mean and std from 0, 1 to 127.5"

This reverts commit 69ceece201174f1b9bf012869e46b13a1fc83261.

preprocessor_config.json

@@ -8,15 +8,15 @@
     "do_rescale": true,
     "do_resize": true,
     "image_mean": [
-      127.5,
-      127.5,
-      127.5
+      0.0,
+      0.0,
+      0.0
     ],
     "image_processor_type": "MobileNetV2ImageProcessor",
     "image_std": [
-      127.5,
-      127.5,
-      127.5
+      1.0,
+      1.0,
+      1.0
     ],
     "resample": 2,
     "rescale_factor": 0.00392156862745098,