Don't crash if process.argv is undefined

[barbogast]

process.argv is undefined within react-native apps. Adding this fallback will prevent has-flag from crashing which in turn allows the usage of packages which use this has-flag (at least if the command line arguments are not important).

In my case I would like to use envalid with react-native. envalid uses chalk, which requires supports-color which finally uses has-flag.

[barbogast]

See also af/envalid#30

[sindresorhus]

This should be fixed in React Native, not in every single module using process.argv. Open an issue on React Native instead.