Update unmerge.cpp - bad number in option 3

src/unmerge.cpp

@@ -78,7 +78,7 @@ void split(int option, int id, vector<string_piece>& v_sp, vector<tagged_lemma>&
         length = v_tr[id].length - 2;
         v_sp.insert(v_sp.begin() + (id+1), string_piece("by"));
         v_tl.insert(v_tl.begin() + (id+1), tagged_lemma("by", "TT-------------"));
-        v_tr.insert(v_tr.begin() + (id+1), token_range(v_tr[id].start+2, size_t(2)));
+        v_tr.insert(v_tr.begin() + (id+1), token_range(v_tr[id].start+length, size_t(2)));
     }
     else if(option == 4) { // Tag VE (wpast)
         c_tag1[1] = 'w';