fix sankey trace x/y node fields #546

Job	Run time
Clippy	3m 35s
Tests (ubuntu-latest)	2m 21s
semver	50s
Tests (macos-latest)	2m 54s
Rustfmt	16s
Tests (windows-latest)	5m 12s
Build Wasm Examples (basic)	48s
Code Coverage	11s
Build Book	1m 35s
Build Examples (basic_charts)	28s
Build Examples (3d_charts)	26s
Build Wasm Examples (callback-example)	52s
Build Examples (scientific_charts)	25s
Build Examples (shapes)	28s
Build Examples (custom_controls)	29s
Build Examples (images)	44s
Build Examples (subplots)	23s
Build Examples (financial_charts)	36s
Build Examples (maps)	42s
Build Examples (kaleido)	1m 26s
Build Examples (ndarray)	30s
	25m 11s

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