update getLedgerEntries documentation (#614)

* update

* update per feedback,

api/methods/getLedgerEntries.mdx

@@ -17,10 +17,11 @@ To fetch contract wasm byte-code, use the ContractCode ledger entry key.
 ## Return
 
 - `<object>`
-  - `entries`: Array containing the specified ledger entries which were found
-    - `key`: `<xdr.LedgerKey>` - The key of the ledger entry (serialized in a base64 string)
-    - `xdr`: `<xdr.LedgerEntryData>` - The current value of the given ledger entry  (serialized in a base64 string)
-    - `lastModifiedLedgerSeq`: `<number>` - The ledger number of the last time this entry was updated (optional)
+  - `entries`: Array containing the specified ledger entries which were found.
+    - `key`: `<xdr.LedgerKey>` - The key of the ledger entry (serialized in a base64 string).
+    - `xdr`: `<xdr.LedgerEntryData>` - The current value of the given ledger entry  (serialized in a base64 string).
+    - `lastModifiedLedgerSeq`: `<string>` - The ledger sequence number of the last time this entry was updated.
+    - `expirationLedgerSeq`: `<string>` - The ledger sequence number after which the ledger entry would expire. This field exists only for ContractCodeEntry and ContractDataEntry ledger entries (optional).
   - `latestLedger`: `<number>` - The current latest ledger observed by the node when this response was generated.
 
 ## Examples
@@ -40,7 +41,8 @@ To fetch contract wasm byte-code, use the ContractCode ledger entry key.
       {
         "key": "AAAAB+qfy4GuVKKfazvyk4R9P9fpo2n9HICsr+xqvVcTF+DC",
         "xdr": "AAAABwAAAADqn8uBrlSin2s78pOEfT/X6aNp/RyArK/sar1XExfgwgAAAAphIGNvbnRyYWN0AAA=",
-        "lastModifiedLedgerSeq": "13"
+        "lastModifiedLedgerSeq": "13",
+        "expirationLedgerSeq": "95"
       }
     ],
     "latestLedger": "179436"
@@ -381,7 +383,8 @@ And the response we get contains (even more) `LedgerEntryData` that we can decod
       {
         "key": "AAAAB2QWKBCU9yGjzDJNxaEZpxEB6A8XsD2S/lKK/sViOLiC",
         "xdr": "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",
-        "lastModifiedLedgerSeq": "75206"
+        "lastModifiedLedgerSeq": "75206",
+        "expirationLedgerSeq": "320384"
       }
     ],
     "latestLedger": "262384"