add nohash=True to elastix num_threads

Author: oesteban

nipype/interfaces/elastix/base.py

@@ -19,5 +19,6 @@
 class ElastixBaseInputSpec(CommandLineInputSpec):
     output_path = Directory('./', exists=True, mandatory=True, usedefault=True,
                             argstr='-out %s', desc='output directory')
-    num_threads = traits.Int(1, argstr='-threads %01d',
-                             desc='set the maximum number of threads of elastix')
+    num_threads = traits.Int(
+        1, argstr='-threads %01d', nohash=True,
+        desc='set the maximum number of threads of elastix')