fixed utf encoding issue

[FarisHijazi]

this fixes issue when generating data for other languages (like arabic)

reproduce issue with:

trdg --count 1000 \
    --length 10 \
    --format 64 \
    --output_dir trdg_data/ids \
    --language ar --font_dir TextRecognitionDataGenerator/trdg/fonts/ar/ \
    --skew_angle 15 --random_skew \
    --random \
    --thread_count 8 \
    --distorsion 3 --distorsion_orientation 2 \
    --background 2 \
    --random_blur \
    --output_bboxes 2

this is now fixed with the encoding='utf8' lines