cwltool/cwlrdf.py: Pass str rather than bytes to write function

Fix output of function in Python 3 runtime

Author: manu-chroma

cwltool/cwlrdf.py

@@ -22,7 +22,7 @@ def visitor(t):
 
 def printrdf(wf, ctx, sr, stdout):
     # type: (Process, ContextType, Text, IO[Any]) -> None
-    stdout.write(gather(wf, ctx).serialize(format=sr))
+    stdout.write(gather(wf, ctx).serialize(format=sr).decode('utf-8'))
 
 
 def lastpart(uri):  # type: (Any) -> Text