解决办法:
在podfile文件中指定source源为master:
source 'https://github.com/CocoaPods/Specs.git'
添加前
target 'Runner' do
use_frameworks!
use_modular_headers!
添加后
source 'https://github.com/CocoaPods/Specs.git'
target 'Runner' do
use_frameworks!
use_modular_headers!