bug fix: Remove the NUL character at the end to avoid JSONDecodeError

[keepcreative]

Remove the NUL character at the end to avoid JSONDecodeError

the code before may cause the error below:

Traceback (most recent call last):
File "/path/to/evaluate.py", line 65, in
eval_res = evaluate_metrics_from_lists(gen_captions, true_captions)
File "/path/to/caption_evaluation_tools/eval_metrics.py", line 156, in evaluate_metrics_from_lists
metrics, per_file_metrics = evaluate_metrics_from_files(
File "/path/to/caption_evaluation_tools/eval_metrics.py", line 102, in evaluate_metrics_from_files
cocoEval.evaluate()
File "/path/to/caption_evaluation_tools/coco_caption/pycocoevalcap/eval.py", line 72, in evaluate
score, scores = scorer.compute_score(gts, res)
File "/path/to/caption_evaluation_tools/coco_caption/pycocoevalcap/spice/spice.py", line 79, in compute_score
results = json.load(data_file)
File "/path/to/miniconda3/envs/myenv/lib/python3.9/json/init.py", line 293, in load
return loads(fp.read(),
File "/path/to/miniconda3/envs/myenv/lib/python3.9/json/init.py", line 346, in loads
return _default_decoder.decode(s)
File "/path/to/miniconda3/envs/myenv/lib/python3.9/json/decoder.py", line 340, in decode
raise JSONDecodeError("Extra data", s, end)
json.decoder.JSONDecodeError: Extra data: line 71062 column 2 (char 1260980)

where the 'Extra data: line 71062 column 2' is actually a NUL symbol.