Update edge.sh

Better edge function:
1) will try to clone the repository to a temp dir;
2) if it succeed, will erase the install dir and move the temp dir to it's place;
3) will create a /tmp/edge_installed, so the source can be updated by a simple git pull;
4) if the clone fails, will remove the temp dir, leaving the current version intact.

This will avoid internet timeout problems and will make the source update faster.