Update requirements.txt

修复运行pip install -r requirements.txt提示ERROR: Invalid requirement: '"detectron2@git+https://github.com/facebookresearch/detectron2.git@v0.6#egg=detectron2"' (from line 4 of requirements.txt)
Hint: = is not a valid operator. Did you mean == ?的错误

requirements.txt

 langchain
 transformers
 unstructured[local-inference]
-"detectron2@git+https://github.com/facebookresearch/detectron2.git@v0.6#egg=detectron2"
+"detectron2@git+https://github.com/facebookresearch/detectron2.git@v0.6#egg=detectron2
 layoutparser[layoutmodels,tesseract]
 nltk
 sentence-transformers