Update lookup-api.md (#763)
Update lookup-api.md (#763)

fix one word '这'
d2l-ai/d2l-zh,mli/gluon-tutorials-zh,mli/gluon-tutorials-zh,mli/gluon-tutorials-zh,mli/gluon-tutorials-zh,d2l-ai/d2l-zh,d2l-ai/d2l-zh