Backend: fix potential parens ambiguity

ElectrumServer.fs had ambiguous parens around the parameters of a function call.
The positioning of the parens has been changed according to the style guide.
If we didn't apply the parens like in this commit, fantomas would cause a
compilation error when trying to format our codebase using our style settings.
(See fsprojects/fantomas#853 for more info.)

src/GWallet.Backend/UtxoCoin/ElectrumServer.fs

@@ -62,7 +62,7 @@ module ElectrumServerSeedList =
         let url = SPrintF1 "https://1209k.com/bitcoin-eye/ele.php?chain=%s" currencyMnemonic
         let web = HtmlWeb()
         let doc = web.Load url
-        let firstTable = doc.DocumentNode.SelectNodes("//table").[0]
+        let firstTable = (doc.DocumentNode.SelectNodes "//table").[0]
         let tableBody = firstTable.SelectSingleNode "tbody"
         let servers = tableBody.SelectNodes "tr"
         seq {