package/mtr: bump to version 0.94

- Add jansson optional dependency:
  https://github.com/traviscross/mtr/commit/c2739eaf139b96f4b4937aee9aa484f0e6d1df55
- Add libgtk3 optional dependency:
  https://github.com/traviscross/mtr/commit/5bd8e6c3ba67fdb9445b1ddc3777aca3b0f7053e


- Update indentation in hash file (two spaces)

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>