chore(deps-dev): Bump @vuepress/theme-default from 2.0.0-rc.55 to 2.0.0-rc.56 in /docs in the vuepress group

chore(deps-dev): Bump @vuepress/theme-default from 2.0.0-rc.55 to 2.0.0-rc.56 in /docs in the vuepress group #495