Make docker requirement an hint

Former-commit-id: ddb86ff8

steps/blsmooth.cwl

@@ -76,12 +76,12 @@ outputs:
     type: Directory
     outputBinding:
       glob: $(inputs.msin.basename)
-
+hints:
+ - class: DockerRequirement
+   dockerPull: 'prefactor:latest'
 requirements:
-- class: DockerRequirement
-  dockerPull: 'prefactor:latest'
-- class: InitialWorkDirRequirement
+ - class: InitialWorkDirRequirement
   listing:
     - entry: $(inputs.msin)
       writable: true
-- class: InlineJavascriptRequirement
+ - class: InlineJavascriptRequirement