Checkpoints update

[HonzaR]

Is your feature request related to a problem? Please describe.

We need to update the checkpoints to prepare for our next SDK release.

Describe the solution you'd like

Instructions:

• https://github.com/zcash/zcash-android-wallet-sdk/blob/main/docs/Architecture.md#checkpoints
• https://github.com/zcash-hackworks/checkmate#usage

Mainnet:

python3 checkmate.py mainnet.lightwalletd.com:9067 --start-height 2232500 --interval 2500 --to-json

Testnet:

python3 checkmate.py lightwalletd.testnet.electriccoin.co:9067 --start-height 2510000 --interval 10000 --to-json