the server installer jar is broken (on linux while installing via command:
java -jar forge-installer.jar --installServer)

i recommend replacing it with this one
https://maven.minecraftforge.net/net/minecraftforge/forge/1.7.10-10.13.4.1614-1.7.10/forge-1.7.10-10.13.4.1614-1.7.10-installer.jar

Have a nice Day