Upgrade go version to 1.18 (#5045)

* Upgrade go version to 1.18

* fix go 1.18 compatibility

* update gofmt

* ignore golangci-lint staticcheck

* update gofmt

vendor/github.com/json-iterator/go/reflect_struct_decoder.go

@@ -1075,6 +1075,11 @@ type stringModeNumberDecoder struct {
 }
 
 func (decoder *stringModeNumberDecoder) Decode(ptr unsafe.Pointer, iter *Iterator) {
+	if iter.WhatIsNext() == NilValue {
+		decoder.elemDecoder.Decode(ptr, iter)
+		return
+	}
+
 	c := iter.nextToken()
 	if c != '"' {
 		iter.ReportError("stringModeNumberDecoder", `expect ", but found `+string([]byte{c}))