cmd/kg/main.go: replace deprecated prom collectors (#255)

Signed-off-by: leonnicolas <leonloechner@gmx.de>

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

@@ -9,6 +9,7 @@ var intDigits []int8
 
 const uint32SafeToMultiply10 = uint32(0xffffffff)/10 - 1
 const uint64SafeToMultiple10 = uint64(0xffffffffffffffff)/10 - 1
+const maxFloat64 = 1<<53 - 1
 
 func init() {
 	intDigits = make([]int8, 256)
@@ -339,7 +340,7 @@ func (iter *Iterator) readUint64(c byte) (ret uint64) {
 }
 
 func (iter *Iterator) assertInteger() {
-	if iter.head < len(iter.buf) && iter.buf[iter.head] == '.' {
+	if iter.head < iter.tail && iter.buf[iter.head] == '.' {
 		iter.ReportError("assertInteger", "can not decode float as int")
 	}
 }