Golang concurrency challenge: make this program finish in 1 second instead of 3.

gistfile1.go

package main

import (
    "time"
    "fmt"
)

//
// Challenge: modify readAllFromOrgs so that the program finishes
// in 1 second instead of 3. 
//
func main() {
  repos := readAllFromOrgs([]string{"microsoft", "yahoo", "google"})
  fmt.Println(repos)
}

// Our own type representing a github repository
type Repo struct {
    Name string
}

//
// Our unoptimized gateway function that calls the Github API.
// This function should be modified such that the call to
// "githubApiListReposByOrg()" is made in parallel. Note that you 
// cannot change this function signature at all.
//
func readAllFromOrgs(orgs []string) []Repo {

  // starting with an empty array of repos
  repos := []Repo{}

  // make calls to the Github API for each Org provided
  for i := range orgs {
    fmt.Println(orgs[i])
    github_repos := githubApiListReposByOrg()
    

    // hydrate array of Repository from github.Repository
    for r := range github_repos {
      repos = append(
        repos,
        Repo{Name: github_repos[r].FullName},
      )
    }
  }

  return repos
}


// 
// BELOW IS LIBRARY CODE, YOU CANNOT EDIT IT.
//

type GithubRepo struct {
    FullName string
}

// Stubbed Github API call. Regularly, this call looks like:
// client.Repositories.ListByOrg(orgs[i], opt).
func githubApiListReposByOrg() []GithubRepo {
    time.Sleep(1000 * time.Millisecond)
    r1 := GithubRepo{FullName: "r1"}
    r2 := GithubRepo{FullName: "r2"}
    return []GithubRepo{r1, r2}
}