Fix time.Parse layout.

[time.Parse](http://godoc.org/time#Parse) expects the layout to have `-0700` and fails when `+0000` is used instead.

E.g.,

```Go
_, err := time.Parse("Mon Jan _2 15:04:05 2006 +0000", "Sun Apr 27 21:26:58 2014 -0500")
if err != nil {
	fmt.Println(err)
}

// Output:
//parsing time "Sun Apr 27 21:26:58 2014 -0700" as "Mon Jan _2 15:04:05 2006 +0000": cannot parse "-0500" as " +0000"
```

```Go
_, err := time.Parse("Mon Jan _2 15:04:05 2006 -0700", "Sun Apr 27 21:26:58 2014 -0500")
if err == nil {
	fmt.Println("ok")
}

// Output:
//ok
```