Defer to native-fetch whenever `ELECTRON_RUN_AS_NODE` is set

You guys are using `electron-fetch` whenever the `is-electron` package detects if it is running in an electron process (particularly, the main process). However, `is-electron` seems to be returning true even when in a process that has been forked from electron's main process as a node server.

This is currently what I am trying to set up in my own application, however, since you can't access electron from within a forked process, attempting to load `electron-fetch` results in an error wherein electron claims that it hasn't been installed properly.

The environment variable `ELECTRON_RUN_AS_NODE` is used to observe when a process is running as a fork from main, so I was thinking an additional condition could be added to defer to `native-fetch` whenever it is set.