Just install electron from the official repository. It’s a metapackage that will pull in the current version, which is electron34. 
sudo pacman -Syu electron
The community repository was merged into the extra repository 2 years ago. When that happened, a pacman.conf.pacnew file was pushed out along with the update, in which the community stanza was removed.
You have obviously not been maintaining your system and merging your .pacnew files, but you are (unfortunately) not alone in this, and so far, the presence of the deprecated community stanza in /etc/pacman.conf had not been throwing any errors, because even though the community repository was empty, it still existed on the mirrors.
With this update however, this is no longer the case. The empty community repository was removed from the mirrors, and that is why you are now seeing those errors.