Add `scaling_ratio` to modify the theta

[Pandede]

Sometimes Predictor will remove part of the license plate number when cropping the image, such like:

It is not conducive to subsequent processes (such as OCR).
Add scaling_ratio to avoid this situation.

[Pandede]

Here is the effect of scaling_ratio:

• Before: scaling_ratio=1.0
  

• After: scaling_ratio=1.2