Reduce number of HDNode tests which cause TravisCI to timeout.
Reduce number of HDNode tests which cause TravisCI to timeout.

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