Added test cases for case-agnostic mnemonics (#557).
Added test cases for case-agnostic mnemonics (#557).

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