Hi I meet this problem when I want to install gel

[Allen1205]

kuma:~ kuma$ brew install gsl
Error: undefined method url' for #<BottleSpecification:0x007f9de2a10d38> Please report this bug: https://git.io/brew-troubleshooting /usr/local/Library/Formula/gsl.rb:6:inblock in class:Gsl'
/usr/local/Library/Homebrew/software_spec.rb:70:in instance_eval' /usr/local/Library/Homebrew/software_spec.rb:70:inbottle'
/usr/local/Library/Homebrew/formula.rb:879:in bottle' /usr/local/Library/Formula/gsl.rb:5:inclass:Gsl'
/usr/local/Library/Formula/gsl.rb:3:in load_file' /usr/local/Library/Homebrew/formulary.rb:92:inmodule_eval'
/usr/local/Library/Homebrew/formulary.rb:92:in load_file' /usr/local/Library/Homebrew/formulary.rb:82:inklass'
/usr/local/Library/Homebrew/formulary.rb:71:in get_formula' /usr/local/Library/Homebrew/formulary.rb:200:infactory'
/usr/local/Library/Homebrew/extend/ARGV.rb:16:in block in formulae' /usr/local/Library/Homebrew/extend/ARGV.rb:16:inmap'
/usr/local/Library/Homebrew/extend/ARGV.rb:16:in formulae' /usr/local/Library/Homebrew/cmd/install.rb:41:ininstall'
/usr/local/Library/brew.rb:135:in `

'
kuma:~ kuma$