Update plugin.json to use staticDirs
Update plugin.json to use staticDirs

instead of staticDir, now deprecated
mpoon/nodebb-plugin-sso-oauth,SIXNetworks/nodebb-plugin-sso-oauth,davidvuong/nodebb-plugin-sso-oauth,Mikodes/nodebb-plugin-sso-oauth,hofkensj/nodebb-plugin-sso-oauth,osufpp/nodebb-plugin-sso-ifsta,julianlam/nodebb-plugin-sso-oauth,Sajan129/nodebb-plugin-sso-oauth,julianlam/nodebb-plugin-sso-wordpress,zerefel/nodebb-plugin-sso-oauth,osufpp/nodebb-plugin-sso-fpp,balasan/yuri-nodebb