Fix OpenCV version assertions in ViTTrack & RAFT and text offset (#234)

* Update OpenCV version assertions for Object Tracking and Optical Flow

* Increased text offset to not overlap with the bounding box.

demo.py

@@ -6,7 +6,7 @@ import numpy as np
 from raft import Raft
 
 # Check OpenCV version
-assert cv.__version__ > "4.9.0", \
+assert cv.__version__ >= "4.9.0", \
        "Please install latest opencv-python to try this demo: python3 -m pip install --upgrade opencv-python"
 
 parser = argparse.ArgumentParser(description='RAFT (https://github.com/princeton-vl/RAFT)')