Update binary submodule to 0.7.3.0 release

One highlight of 0.7.3.0 is the new instance for `Natural` (cherry picked from commit f2867dc5)

Update binary submodule to 0.7.3.0 release
a2858b82 · Herbert Valerio Riedel · bcfe5344 · ff9a48fb · a3edce4b · ff9a48fb
Commit a2858b82 authored 10 years ago by Herbert Valerio Riedel
--- a/binary @ ff9a48fb
+++ b/binary @ ff9a48fb
-Subproject commit a3edce4b95b82388997929424ce98b1d7a75350d
+Subproject commit ff9a48fb213c2d1fd2e58b19c92264a3efadff7a