optimize help output

optimize help output
shasum:

68591f03e04ec0423f83305c1d3bf7d5070cfe81 rsock-Darwin-x86_64-20180307.zip
39e93b2c8bd140f5795cddcda8d168a18ea7abaa rsock-Linux-x86_64-20180307.tar.gz

first release

first release. 开了-O2，传入错误参数会崩溃-_-。传入正确的参数即可