Fix saving system config file
Fix saving system config file

See https://github.com/FreshRSS/FreshRSS/issues/730

asmundg/FreshRSS,Dolomich/FreshRSS,FreshRSS/FreshRSS,Alkarex/FreshRSS,Alkarex/FreshRSS,FreshRSS/FreshRSS,aledeg/FreshRSS,romibi/FreshRSS,aledeg/FreshRSS,superboum/FreshRSS,romibi/FreshRSS,marienfressinaud/FreshRSS,Alkarex/FreshRSS,samuelstein/FreshRSS,romibi/FreshRSS,Alkarex/FreshRSS,asmundg/FreshRSS,aledeg/FreshRSS,superboum/FreshRSS,asmundg/FreshRSS,samuelstein/FreshRSS,Dolomich/FreshRSS,aledeg/FreshRSS,samuelstein/FreshRSS,FreshRSS/FreshRSS,Dolomich/FreshRSS,FreshRSS/FreshRSS,superboum/FreshRSS,marienfressinaud/FreshRSS,marienfressinaud/FreshRSS,marienfressinaud/FreshRSS,romibi/FreshRSS