DOC: fix obsolete URL (#39999)

https://github.com/trifacta/vega -> https://github.com/vega/vega

Author: partev

doc/source/ecosystem.rst

@@ -156,7 +156,7 @@ A good implementation for Python users is `has2k1/plotnine <https://github.com/h
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 `IPython Vega <https://github.com/vega/ipyvega>`__ leverages `Vega
-<https://github.com/trifacta/vega>`__ to create plots within Jupyter Notebook.
+<https://github.com/vega/vega>`__ to create plots within Jupyter Notebook.
 
 `Plotly <https://plot.ly/python>`__
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