Log Message:
fluidsynth: Update to 2.1.

Changes:

- a regression introduced in 2.1.0 caused the jack audio driver to not correct a \ 
sample-rate mismatch (#607)
- pkg-config is now being to used to find readline (#606, thanks to @ffontaine)
- fix various typos in the documentation (#600, thanks to @luzpaz)
- fix a memory leak in the file renderer
- fix leaking memory when sequencer clients were not explicitly unregistered (#610)
- fix a heap-based use-after-free in jack driver (#613)
- fix the linker possibly not finding libinstpatch (#617, thanks to @realnc)