getHash(key) {
		const hash = crypto.createHash("md5").update(key).digest("hex");
		const hashNum = parseInt(hash.substring(0, 8), 16);
		return this.opts.ringSize ? hashNum % this.opts.ringSize : hashNum;
	}
Calculate 8 bit integer hash from string key based on MD5 hash.

@param {String} key
@returns {Number}
@memberof ShardStrategy