loveyacper/raft_for_dummies: src/mapreduce/common_map.go; 12 LoC

Found a possible issue in [loveyacper/raft_for_dummies](https://www.github.com/loveyacper/raft_for_dummies) at [src/mapreduce/common_map.go](https://github.com/loveyacper/raft_for_dummies/blob/30047f10b2e9851ac17cc006e2ce38486d37de8c/src/mapreduce/common_map.go#L27-L38)

Below is the message reported by the analyzer for this snippet of code. Beware that the analyzer only reports the first
issue it finds, so please do not limit your consideration to the contents of the below message.

> function call at line 36 may store a reference to kv

[Click here to see the code in its original context.](https://github.com/loveyacper/raft_for_dummies/blob/30047f10b2e9851ac17cc006e2ce38486d37de8c/src/mapreduce/common_map.go#L27-L38)

Click here to show the 12 line(s) of Go which triggered the analyzer.

```go
for _ , kv := range kvs {
reduceTask := ihash(kv.Key) % nReduce
var intermediate string = reduceName(jobName, mapTask, reduceTask) // intermediate file
f, err := os.OpenFile(intermediate, os.O_APPEND|os.O_CREATE|os.O_RDWR, 0666)
if err != nil {
fmt.Println("open err " + err.Error())
}

enc := json.NewEncoder(f)
enc.Encode(&kv)
f.Close()
}

```

Leave a reaction on this issue to contribute to the project by classifying this instance as a **Bug** :-1:, **Mitigated** :+1:, or **Desirable Behavior** :rocket:
See the descriptions of the classifications [here](https://github.com/github-vet/rangeclosure-findings#how-can-i-help) for more information.

commit ID: 30047f10b2e9851ac17cc006e2ce38486d37de8c