message: feat: update to mainnet urls
diff: @@ -38,7 +38,7 @@ export interface StacksNetwork {
  export class StacksMainnet implements StacksNetwork {
  version = TransactionVersion.Mainnet;
  chainId = ChainID.Mainnet;
  - coreApiUrl = 'https://core.blockstack.org';
  + coreApiUrl = 'https://stacks-node-api.mainnet.stacks.co';
  broadcastEndpoint = '/v2/transactions';
  transferFeeEstimateEndpoint = '/v2/fees/transfer';
  accountEndpoint = '/v2/accounts';
  @@ -97,7 +97,7 @@ export class StacksMainnet implements StacksNetwork {
  export class StacksTestnet extends StacksMainnet implements StacksNetwork {
  version = TransactionVersion.Testnet;
  chainId = ChainID.Testnet;
  - coreApiUrl = 'https://stacks-node-api.blockstack.org';
  + coreApiUrl = 'https://stacks-node-api.testnet.stacks.co';
  }
  export class StacksMocknet extends StacksMainnet implements StacksNetwork {
  