Anchors are broken for MapSlice

[sam701]

Unmarshal produces wrong output for yaml.MapSlice. Here is the code:

package main

import (
	"log"

	"gopkg.in/yaml.v2"
)

var content = `
a1:
  f1: value1
  <<: &anchor
    f2: value2
  
a2:
  f3: value3
  <<: *anchor
`

func main() {
	var result map[interface{}]interface{}
	yaml.Unmarshal([]byte(content), &result)
	log.Println(result)

	var result2 yaml.MapSlice
	yaml.Unmarshal([]byte(content), &result2)
	log.Println(result2)
}

Output:

2018/03/19 10:37:04 map[a1:map[f1:value1 f2:value2] a2:map[f3:value3 f2:value2]]
2018/03/19 10:37:04 [{a1 [{f1 value1}]} {a2 [{f3 value3}]}]

f2 is missing for yaml.MapSlice.

[niemeyer]

That's #184.