Correct the spelling of "instuct"

[zzz47zzz]

When finetuning on flickr30k, an error occurs because the code loads "configs/datasets/flickr30k/defaults_cap_instuct.yaml" according to the path defined in lavis/datasets/builders/caption_builder.py. Then, I find that the spelling of "instuct" is wrong and correct the spelling error.

[salesforce-cla]

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