chore: fix the broken links in the document. (#365)

# What ❔

- Fix the broken links in the document.

## Why ❔

- Can't open

## Checklist

<!-- Check your PR fulfills the following items. -->
<!-- For draft PRs check the boxes as you complete them. -->

- [x] PR title corresponds to the body of PR (we generate changelog
entries from PRs).
- [x] Tests for the changes have been added / updated.
- [x] Documentation comments have been added / updated.
- [x] Code has been formatted via `zk fmt` and `zk lint`.

docs/advanced/gas_and_fees.md

@@ -124,10 +124,10 @@ There are a few reasons why refunds might be 'larger' on zkSync (i.e., why we mi
   impacts the amount of gas used by pubdata.
 
 [main_node_fetcher]:
-  https://github.com/matter-labs/zksync-2-dev/blob/d590b3f0965a23eb0011779aab829d86d4fdc1d1/core/bin/zksync_core/src/l1_gas_price/main_node_fetcher.rs#L33
+  https://github.com/matter-labs/zksync-era/blob/main/core/lib/zksync_core/src/l1_gas_price/main_node_fetcher.rs#L32
   'main node fetcher'
 [gas_adjuster]:
-  https://github.com/matter-labs/zksync-2-dev/blob/d590b3f0965a23eb0011779aab829d86d4fdc1d1/core/bin/zksync_core/src/l1_gas_price/gas_adjuster/mod.rs#L25
+  https://github.com/matter-labs/zksync-era/blob/main/core/lib/zksync_core/src/l1_gas_price/gas_adjuster/mod.rs#L30
   'gas_adjuster'
 [get_txs_fee_in_wei]:
   https://github.com/matter-labs/zksync-era/blob/d590b3f0965a23eb0011779aab829d86d4fdc1d1/core/bin/zksync_core/src/api_server/tx_sender/mod.rs#L450