Change newline style dos unix lf crlf

ref: https://stackoverflow.com/questions/2613800/how-to-convert-dos-windows-newline-crlf-to-unix-newline-lf

ref: https://unix.stackexchange.com/questions/32001/what-is-m-and-how-do-i-get-rid-of-it

在 vim 中执行以下两行可以把 dos 类型的 CRLF 改为 unix LF:

:set ff=unix
:e ++ff=dos