Update Bookstack to 0.22.0#86

Merged

solidnerd merged 2 commits intosolidnerd:masterfrom

pschmitt:v0.22.0

Jun 5, 2018

Commits on May 29, 2018

Update Booktstack to 0.22.0
pschmitt
committed

Commits on May 30, 2018

Replace libpng12-dev with libpng-dev
pschmitt
committed