docbook-mathml: fix an indentation mistake
docbook-mathml: fix an indentation mistake

Signed-off-by: Johannes Schindelin <53fb8db7833fca1e1746dd8592f61048d350f64c@gmx.de>

JPeterMugaas/MSYS2-packages,mati865/MSYS2-packages,waterlan/MSYS2-packages,JPeterMugaas/MSYS2-packages,waterlan/MSYS2-packages,mati865/MSYS2-packages,waterlan/MSYS2-packages,JPeterMugaas/MSYS2-packages,mati865/MSYS2-packages,JPeterMugaas/MSYS2-packages,waterlan/MSYS2-packages,mati865/MSYS2-packages