add IGNORE_UNICODE flag to doctest (py27 compat)

Author: oesteban

nipype/interfaces/fsl/possum.py

@@ -79,7 +79,7 @@ class B0Calc(FSLCommand):
     >>> b0calc = B0Calc()
     >>> b0calc.inputs.in_file = 'tissue+air_map.nii'
     >>> b0calc.inputs.z_b0 = 3.0
-    >>> b0calc.cmdline
+    >>> b0calc.cmdline  # doctest: +IGNORE_UNICODE
     'b0calc -i tissue+air_map.nii -o tissue+air_map_b0field.nii.gz --b0=3.00'
 
     """