doc: fix typo variant_classification -> variant_classifications

Author: corneliusroemer

README.md

@@ -54,10 +54,10 @@ To run pipeline for all available data generated by ingest:
 nextstrain build .
 ```
 
-To run the pipeline for specific data provenance, variant classification and geo resolution (e.g. gisaid, nextstrain_clades and global only):
+To run the pipeline for specific data provenance, variant classifications and geo resolution (e.g. gisaid, nextstrain_clades and global only):
 
 ```bash
-nextstrain build . --configfile config/config.yaml --config data_provenances=gisaid variant_classification=nextstrain_clades geo_resolutions=global
+nextstrain build . --configfile config/config.yaml --config data_provenances=gisaid variant_classifications=nextstrain_clades geo_resolutions=global
 ```
 
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