function getRuleRegExp(command) {
	return new RegExp(`\\b${command.split(' ').shift()}\\b`);
}
Generate a regular expression to detect a rule in existing rules. For simplicity
assumes that the first word in the command is the binary you're running.

Example: 'eslint --fix' -> /\beslint\b/

TODO: Allow overriding for more complex commands

@param {string} command