In Windows, env variables that represent a list (such as PATH or NODE_PATH) separate their elements
using a semicolon(;), but in UNIX they're separated using a colon (:).

This commit adds a conversion layer, so regardless of how the delimiter is written when calling
cross-env, it will be converted to the correct platform delimiter at runtime. To interpret a colon/semicolon
literally instead, preced it with a backslash, like this: "cross-env VAR=semi\\;colon\\:"

BREAKING CHANGE: If an env variable has : or ; in its value, it will be converted to : on UNIX
systems or ; on Windows systems. To keep the old functionality, you will need to escape those
characters with a backslash.

kentcdodds#80

…-style), not the other way around