Update block explorer in nano.dart

Replace NanoLooker (down) with Nanexplorer.

(cherry picked from commit 193a0b5)

Author: Verycutecat

lib/wallets/crypto_currency/coins/nano.dart

@@ -95,7 +95,7 @@ class Nano extends NanoCurrency {
   Uri defaultBlockExplorer(String txid) {
     switch (network) {
       case CryptoCurrencyNetwork.main:
-        return Uri.parse("https://www.nanolooker.com/block/$txid");
+        return Uri.parse("https://nanexplorer.com/nano/blocks/$txid");
       default:
         throw Exception(
           "Unsupported network for defaultBlockExplorer(): $network",