Fix whitespace error

CHANGELOG.md

@@ -12,7 +12,7 @@ This release of std++ was managed by Ralf Jung, Robbert Krebbers, and Tej
 Chajed, with contributions from Alix Trieu, Andrej Dudenhefner, Dan Frumin,
 Fengmin Zhu, Hoang-Hai Dang, Jan, Lennard Gäher, Michael Sammler, Paolo G.
 Giarrusso, Ralf Jung, Robbert Krebbers, Simon Friis Vindum, Simon Gregersen,
-and Tej Chajed.  Thanks a lot to everyone involved!
+and Tej Chajed. Thanks a lot to everyone involved!
 
 - Remove singleton notations `{[ x,y ]}` and `{[ x,y,z ]}` for `{[ (x,y) ]}`
   and `{[ (x,y,z) ]}`. They date back to the time we used the `singleton` class