Added Retry-After support and adjustable slot interval to fetchJson.
Added Retry-After support and adjustable slot interval to fetchJson.

ethers-io/ethers.js,ethers-io/ethers.js,ethers-io/ethers.js,ethers-io/ethers.js,ethers-io/ethers.js,ethers-io/ethers.js,ethers-io/ethers.js