Fix typo in README.md for 'tskit' format

[hyanwong]

No description provided.

[hyanwong]

Missed another quote - somehow this was created not in my fork, so I will close an open another

[hyanwong]

Oh no, actually it was fine, sorry - reopening.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.76%. Comparing base (6b6156c) to head (e0a31cc).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3349   +/-   ##
=======================================
  Coverage   89.76%   89.76%           
=======================================
  Files          29       29           
  Lines       31292    31292           
  Branches     5738     5738           
=======================================
  Hits        28089    28089           
  Misses       1794     1794           
  Partials     1409     1409           

Flag	Coverage Δ
c-tests	86.77% <ø> (ø)
lwt-tests	80.38% <ø> (ø)
python-c-tests	87.12% <ø> (ø)
python-tests	98.85% <ø> (ø)
python-tests-no-jit	33.51% <ø> (ø)
python-tests-numpy1	50.28% <ø> (ø)

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[jeromekelleher]

LGTM - made an unrelated suggestion while you're in there.