Update vendor directory and make necessary code changes

Fixes for new geth version

pkg/geth/blockchain.go

@@ -150,6 +150,10 @@ func (blockChain *BlockChain) getPOAHeader(blockNumber int64) (header core.Heade
 	if POAHeader.Number == nil {
 		return header, ErrEmptyHeader
 	}
+	time := POAHeader.Time.ToInt()
+	if time == nil {
+		time = big.NewInt(0)
+	}
 	return blockChain.headerConverter.Convert(&types.Header{
 		ParentHash:  POAHeader.ParentHash,
 		UncleHash:   POAHeader.UncleHash,

pkg/geth/converters/common/header_converter.go

@@ -31,6 +31,7 @@ func (converter HeaderConverter) Convert(gethHeader *types.Header, blockHash str
 	if err != nil {
 		panic(err)
 	}
+	strInt := strconv.FormatUint(gethHeader.Time, 10)
 	coreHeader := core.Header{
 		Hash:        blockHash,
 		BlockNumber: gethHeader.Number.Int64(),