Updated CHANGELOG

(cherry picked from commit 9c375231)

CHANGELOG.md

@@ -6,6 +6,7 @@ v4.3.2
 **Library**:
 - Add small optimisation for DriverAdaptive (!618)
 - Updated FFTW build to use the compiler used for building Nektar++ (!629)
+- Fix numbering bug in periodic boundary conditions (!631)
 
 **Packaging**:
 - Fixes for DEB package dependencies (!630)