fix: update BIDS derivatives links

Author: oesteban

docs/assets/bhd2020/presentation.md

@@ -196,7 +196,7 @@ Around 50% of teams used *fMRIPrep*'ed inputs.
 ### fMRIPrep produces analysis-ready data from diverse data
 * minimal requirements ([BIDS-compliant](https://bids-standard.github.io/bids-validator/));
 * *agnostic* to downstream steps of the workflow
-  * produces [BIDS-Derivatives](https://bids-specification.readthedocs.io/en/derivatives/05-derivatives/01-introduction.html);
+  * produces [BIDS-Derivatives](https://bids-specification.readthedocs.io/en/stable/derivatives/introduction.html);
 * robust against inhomogeneity of data across studies
 
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docs/assets/torw2020/presentation.md

@@ -103,7 +103,7 @@ template: sidebar
 ### fMRIPrep produces analysis-ready data from acquired (fMRI) data
 * minimal requirements ([BIDS-compliant](https://bids-standard.github.io/bids-validator/));
 * *agnostic* to downstream steps of the workflow
-  * produces [BIDS-Derivatives](https://bids-specification.readthedocs.io/en/derivatives/05-derivatives/01-introduction.html);
+  * produces [BIDS-Derivatives](https://bids-specification.readthedocs.io/en/stable/derivatives/introduction.html);
 
 ???