Use Filter object in testGetNSignicativeKmers

Since the function testGetNSignificativeKmers in testFilter was
using pair and not Filter object, it now use the filter object getter for
the pair.

For more informations, see #3283.

algo/tests/unit-tests/testFilter.cpp

@@ -362,7 +362,8 @@ void testGetNSignicativeKmers(){
 
   for(int i = 0; i < germline.rep_5.size(); ++i){
     Sequence seq = germline.rep_5.read(i);
-    filtered = filterBioReaderWithACAutomaton(germline.automaton_5, germline.rep_5, seq.sequence, 1);
+    FilterWithACAutomaton *f = germline.getFilter();
+    filtered = f->filterBioReaderWithACAutomaton(germline.rep_5, seq.sequence, 1);
     int j = 0;
     while(j < filtered.size()){
       if(extractGeneName(filtered.label(j)) == extractGeneName(seq.label)){