Update minimum nextflow version

nextflow.config

@@ -133,5 +133,5 @@ manifest {
   description = 'This pipeline was created to be a standard mRNA-sequencing analysis pipeline which integrates with the GUDMAP and RBK consortium data-hub.'
   mainScript = 'rna-seq.nf'
   version = 'v2.0.0'
-  nextflowVersion = '>=19.09.0'
+  nextflowVersion = '>=20.01.0'
 }