fix return type of PullRequests.ListCommits

this method actually returns RepositoryCommits (go-github's term for
this, not GitHub's) rather than Commits.  They are very, very close in
structure (which is likely why this has gone unnoticed for so long), one
of the primary differences being that RepositoryCommits exposes the
GitHub identity of the commit author and committer if possible.

github/pulls.go

@@ -169,7 +169,7 @@ func (s *PullRequestsService) Edit(owner string, repo string, number int, pull *
 // ListCommits lists the commits in a pull request.
 //
 // GitHub API docs: https://developer.github.com/v3/pulls/#list-commits-on-a-pull-request
-func (s *PullRequestsService) ListCommits(owner string, repo string, number int, opt *ListOptions) ([]Commit, *Response, error) {
+func (s *PullRequestsService) ListCommits(owner string, repo string, number int, opt *ListOptions) ([]RepositoryCommit, *Response, error) {
 	u := fmt.Sprintf("repos/%v/%v/pulls/%d/commits", owner, repo, number)
 	u, err := addOptions(u, opt)
 	if err != nil {
@@ -181,7 +181,7 @@ func (s *PullRequestsService) ListCommits(owner string, repo string, number int,
 		return nil, nil, err
 	}
 
-	commits := new([]Commit)
+	commits := new([]RepositoryCommit)
 	resp, err := s.client.Do(req, commits)
 	if err != nil {
 		return nil, resp, err

github/pulls_test.go

@@ -205,8 +205,8 @@ func TestPullRequestsService_ListCommits(t *testing.T) {
 		t.Errorf("PullRequests.ListCommits returned error: %v", err)
 	}
 
-	want := []Commit{
-		Commit{
+	want := []RepositoryCommit{
+		{
 			SHA: String("3"),
 			Parents: []Commit{
 				Commit{
@@ -214,7 +214,7 @@ func TestPullRequestsService_ListCommits(t *testing.T) {
 				},
 			},
 		},
-		Commit{
+		{
 			SHA: String("2"),
 			Parents: []Commit{
 				Commit{

tests/integration/pulls_test.go

@@ -0,0 +1,23 @@
+// Copyright 2014 The go-github AUTHORS. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tests
+
+import "testing"
+
+func TestPullRequests_ListCommits(t *testing.T) {
+	commits, _, err := client.PullRequests.ListCommits("google", "go-github", 2, nil)
+	if err != nil {
+		t.Fatalf("PullRequests.ListCommits() returned error: %v", err)
+	}
+
+	if got, want := len(commits), 3; got != want {
+		t.Fatalf("PullRequests.ListCommits() returned %d commits, want %d", got, want)
+	}
+
+	if got, want := *commits[0].Author.Login, "sqs"; got != want {
+		t.Fatalf("PullRequests.ListCommits()[0].Author.Login returned %v, want %v", got, want)
+	}
+}