Iterating over the answer from Tao-Nhan Nguyen, accounting the original value set for every pod, adjusting it only if it's not greater than 8.0... Add the following to the Podfile:
post_install do |installer|
installer.pods_project.targets.each do |target|
target.build_configurations.each do |config|
if Gem::Version.new('8.0') > Gem::Version.new(config.build_settings['IPHONEOS_DEPLOYMENT_TARGET'])
config.build_settings['IPHONEOS_DEPLOYMENT_TARGET'] = '8.0'
end
end
end
end