add CDN downloading link for openh264v1.7.0
add CDN downloading link for openh264v1.7.0

mstorsjo/openh264,shihuade/openh264,mstorsjo/openh264,cisco/openh264,GuangweiWang/openh264,shihuade/openh264,shihuade/openh264,ruil2/openh264,ruil2/openh264,cisco/openh264,sijchen/openh264,ruil2/openh264,shihuade/openh264,GuangweiWang/openh264,ruil2/openh264,sijchen/openh264,GuangweiWang/openh264,cisco/openh264,ruil2/openh264,sijchen/openh264,GuangweiWang/openh264,cisco/openh264,shihuade/openh264,mstorsjo/openh264,mstorsjo/openh264,shihuade/openh264,sijchen/openh264,GuangweiWang/openh264,shihuade/openh264,cisco/openh264,mstorsjo/openh264,cisco/openh264,GuangweiWang/openh264,GuangweiWang/openh264,ruil2/openh264,sijchen/openh264,mstorsjo/openh264,cisco/openh264,ruil2/openh264,sijchen/openh264,mstorsjo/openh264,sijchen/openh264