For fellow vimrc noobs / lazy people such as myself, the fix for 1.7.4 (removed the 2 intermediate mappings as well):
exmap blankBelow obcommand obsidian-editor-shortcuts:insertLineBelow
exmap blankAbove obcommand obsidian-editor-shortcuts:insertLineAbove
nmap o :blankBelow<CR>i
nmap O :blankAbove<CR>i