The first time that Forge runs it needs to download a bunch of code libraries that match your system. One of these is failing to download for some reason, and it's required for Forge to run. I can download it in my browser though, so whatever is preventing Forge from downloading it automatically isn't preventing me from downloading it manually.
So here's how you may be able to fix it:
Download the library manually. (That's the same link as in the error message in your question.)
This will download a file named
scala-library-2.10.2.jar. Save it somewhere where you can find it again.
Open your .minecraft folder, then navigate to libraries → org .
Inside the org folder, create the folder
Open the new scala-lang folder and create the folder
scala-library inside it.
Open the new scala-library and create the folder
2.10.2 inside it.
Open the new 2.10.2 folder. Find
scala-library-2.10.2.jar wherever you saved it in step
(1), and put it inside 2.10.2.
Now double-check that all the folders are named exactly as above, with no extra letters, and no spaces before or after each folder name. Any errors will prevent the next step from working. Fix any naming errors you find before moving on.
Run the launcher and start Forge. When it gets to the point where it used to try downloading Scala, it should find the library you just manually installed and keep going.