Add new endpoint getWalletBalance

See: https://github.com/bybit-exchange/bybit-official-api-docs/blob/master/en/CHANGELOG.md#2020-02-10

lib/rest-client.js

@@ -144,6 +144,12 @@ module.exports = class RestClient {
     return await this.request.get('/open-api/wallet/withdraw/list', params);
   }
 
+  async getWalletBalance(params) {
+    assert(params, 'No params passed');
+    assert(params.coin, 'Parameter coin is required');
+    return await this.request.get('/v2/private/wallet/balance', params);
+  }
+
   async setRiskLimit(params) {
     assert(params, 'No params passed');
     assert(params.symbol, 'Parameter symbol is required');