Fixing compilation errors with newer gcc versions.

[snehring]

Newer gcc versions error out on the std::shared_ptr references in analysis/SatsumaSynteny2.cc without this header.

/home/snehring/projects/satsuma2/analysis/SatsumaSynteny2.cc:154:26: error: ‘shared_ptr’ is not a member of ‘std’
  154 |       match_blocks= std::shared_ptr<std::vector<match_segments>>(new vector<match_segments>());
      |                          ^~~~~~~~~~
/home/snehring/projects/satsuma2/analysis/SatsumaSynteny2.cc:154:26: note: ‘std::shared_ptr’ is defined in header ‘<memory>’; did you forget to ‘#include <memory>’?