Like it mentions, it cannot correctly download the guava file, possibly because your computer is blocking permissions to download it. You either need to manually download it and place it in the specified directory, or find a way to allow it to download (probably via firewall or antivirus).
It might help also to delete the old corrupt file from .minecraft/libraries/com/google/guava/guava/21.0/ (this is where the new file should manually be placed).