fix: allow echo.cwl to run on python3

Author: psafont

tests/wf/echo.cwl

@@ -5,8 +5,9 @@ inputs:
   script:
     type: string
     default: |
+      from __future__ import print_function
       import sys
-      print sys.argv[1]
+      print(sys.argv[1])
       if sys.argv[1] == "2":
         exit(1)
       else:
@@ -19,4 +20,4 @@ outputs:
     type: File
     outputBinding:
       glob: foo$(inputs.r).txt
-arguments: [python, -c, $(inputs.script), $(inputs.r)]
+arguments: [python, -c, $(inputs.script), $(inputs.r)]