fix(RetroPath2): remove regex deprecation warning

using raw string r"..."

retropath2_wrapper/RetroPath2.py

@@ -348,7 +348,7 @@ def check_inchi_from_file(
             #       Other (sub-)layers
             #       matches:
             #           (/.+)? --> if '/' is present, then at least one character/symbol is mandatory
-            if match('InChI=1(S)?/(([a-z|[A-Z])+\d*)+(/.+)?$', inchi) is None:
+            if match(r'InChI=1(S)?/(([a-z|[A-Z])+\d*)+(/.+)?$', inchi) is None:
                 logger.error('        {inchi} is not a valid InChI notation'.format(inchi=inchi))
                 return ''