fix typo

Author: Remi-Gau

src/spm_2_bids.m

@@ -69,7 +69,7 @@
     % TODO implement methods in Mapping to filter by suffix / extention /
     % entities
 
-    % if any suffix / extention mentioned in the mapping we check for that as well
+    % if any suffix / extension mentioned in the mapping we check for that as well
     % if none is mentioned anywhere in the mapping then anything goes
     suffix_match = true(size(mapping));
     if ~all(cellfun('isempty', {mapping.suffix}'))