[FLINK-20362][doc] Fix broken link in sourceSinks.zh.md

[fsk119]

What is the purpose of the change

Fix broken link {% link dev/table/legacySourceSinks.md %} ->({% link dev/table/legacySourceSinks.zh.md %})

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Last check on commit e0e112b (Thu Nov 26 02:48:31 UTC 2020)

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[leonardBang]

LGTM

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CI report:

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[dianfu]

LGTM. Merging...