scripted-diff: Avoid interface keyword to fix windows gitian build

Rename `interface` to `interfaces`

Build failure reported by Chun Kuan Lee <ken2812221@gmail.com>
https://github.com/bitcoin/bitcoin/pull/10244#issuecomment-379434756

-BEGIN VERIFY SCRIPT-

git mv src/interface src/interfaces
ren() { git grep -l "$1" | xargs sed -i "s,$1,$2,g"; }
ren interface/            interfaces/
ren interface::           interfaces::
ren BITCOIN_INTERFACE_    BITCOIN_INTERFACES_
ren "namespace interface" "namespace interfaces"

-END VERIFY SCRIPT-

src/qt/sendcoinsentry.cpp

@@ -127,7 +127,7 @@ void SendCoinsEntry::useAvailableBalanceClicked()
     Q_EMIT useAvailableBalance(this);
 }
 
-bool SendCoinsEntry::validate(interface::Node& node)
+bool SendCoinsEntry::validate(interfaces::Node& node)
 {
     if (!model)
         return false;