ipfx/bin/make_stimulus_ontology.py: Avoid unknown escape sequence

This fixes the warning:

  /home/thomas/devel/ipfx/ipfx/bin/make_stimulus_ontology.py:26: DeprecationWarning: invalid escape sequence \d
    m = re.search("(.*)\d{6}$", scode)

Author: t-b

ipfx/bin/make_stimulus_ontology.py

@@ -23,7 +23,7 @@ def make_stimulus_ontology(stims):
         scode = stim['stimulus_code']
 
         # code tags
-        m = re.search("(.*)\d{6}$", scode)
+        m = re.search(r"(.*)\d{6}$", scode)
         if m:
             code_name, = m.groups()
             tags.add((CODE, code_name, scode))