Fix ERR_INVALID_ARG_TYPE error on Windows

Currently if the user doesn't have the HOME env var set they get the following error when running gsts

internal/validators.js:117
    throw new ERR_INVALID_ARG_TYPE(name, 'string', value);
    ^
TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string. Received undefined
    at validateString (internal/validators.js:117:11)
    at Object.join (path.js:375:7)
    at Object.<anonymous> (C:\Users\--\AppData\Roaming\npm\node_modules\gsts\index.js:42:45)
    at Module._compile (internal/modules/cjs/loader.js:1158:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1178:10)
    at Module.load (internal/modules/cjs/loader.js:1002:32)
    at Function.Module._load (internal/modules/cjs/loader.js:901:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:74:12)
    at internal/main/run_main_module.js:18:47 {
  code: 'ERR_INVALID_ARG_TYPE'

Made a small change to make it so the plist file path generation doesn't crash on windows.

ruimarinho / gsts

Fix ERR_INVALID_ARG_TYPE error on Windows #4