Hello,
I can answer you I think, because I have the same problem with my launcher.
Basically, scala lib disappear from forge website, you can't find it anymore here: http://files.minecraftforge.net/maven/ in "org" directory, as your log confirm:
"Couldn't get hash for org/scala-lang/scala-xml_2.11/1.0.2/scala-xml_2.11-1.0.2.jar from https://modloaders.cursecdn.com/647622546/maven/org/scala-lang/scala-xml_2.11/1.0.2/scala-xml_2.11-1.0.2.jar.sha1: HTTP 404: Not Found"
It works with your friend because I think he downloaded the game before the deletion of this lib, so he already have it in his game folder so forge doesn't redownload it.
I will try to know why this disappear, and if it's normal or not (I haven't searched on this forum yet).
EDIT: It seems it could be because Forge 1.7.10 (or 1.11) isn't supported anymore, I think they deleted the old lib download location, because it shouldn't be use anymore. It download without problems with up-to-date forge version.
EDIT2: My answer is a bit late, but if it can help someone with a similar problem, it worth it I think
