latest vmaf version not supported

[13905182381]

in vmaf_calculate.py, there is a sentense
cmd = "./vmaf/run_vmaf"

however, in latest vmaf, there is no run_vmaf in vmaf folder anymore, so it will break build. I should mannually set vmaf build to old version like 1.3.14.

suggest support latest vmaf, or write version 1.3.14 clearly into readme.

[AliceCodeZhang]

Thanks for comments, we will update the documents