Convert input image to RGB

This adds support for input images with different encodings.

The classification version already does this: https://github.com/google-coral/tflite/blob/master/python/examples/classification/classify_image.py#L103

Author: maxbbraun

python/examples/detection/detect_image.py

@@ -94,7 +94,7 @@ def main():
   interpreter = make_interpreter(args.model)
   interpreter.allocate_tensors()
 
-  image = Image.open(args.input)
+  image = Image.open(args.input).convert('RGB')
   scale = detect.set_input(interpreter, image.size,
                            lambda size: image.resize(size, Image.ANTIALIAS))