Allows default branch to be set to master on update

https://github.com/terraform-providers/terraform-provider-github/pull/194

github/resource_github_repository.go

@@ -348,10 +348,7 @@ func resourceGithubRepositoryUpdate(d *schema.ResourceData, meta interface{}) er
 	// Can only set `default_branch` on an already created repository with the target branches ref already in-place
 	if v, ok := d.GetOk("default_branch"); ok {
 		branch := v.(string)
-		// If branch is "master", and the repository hasn't been initialized yet, setting this value will fail
-		if branch != "master" {
-			repoReq.DefaultBranch = &branch
-		}
+		repoReq.DefaultBranch = &branch
 	}
 
 	repoName := d.Id()

github/resource_github_repository_test.go

@@ -321,6 +321,26 @@ func TestAccGithubRepository_defaultBranch(t *testing.T) {
 					}),
 				),
 			},
+			{
+				Config: testAccGithubRepositoryUpdateConfigMasterDefaultBranch(randString),
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckGithubRepositoryExists("github_repository.foo", &repo),
+					testAccCheckGithubRepositoryAttributes(&repo, &testAccGithubRepositoryExpectedAttributes{
+						Name:             name,
+						Description:      "Updated " + description,
+						Homepage:         "http://example.com/",
+						AutoInit:         true,
+						HasIssues:        true,
+						HasWiki:          true,
+						AllowMergeCommit: true,
+						AllowSquashMerge: false,
+						AllowRebaseMerge: false,
+						HasDownloads:     true,
+						DefaultBranch:    "master",
+						Archived:         false,
+					}),
+				),
+			},
 			{
 				ResourceName:      rn,
 				ImportState:       true,
@@ -859,6 +879,29 @@ resource "github_repository" "foo" {
 `, randString, randString)
 }
 
+func testAccGithubRepositoryUpdateConfigMasterDefaultBranch(randString string) string {
+	return fmt.Sprintf(`
+resource "github_repository" "foo" {
+  name = "tf-acc-test-%s"
+  description = "Updated Terraform acceptance tests %s"
+  homepage_url = "http://example.com/"
+
+  # So that acceptance tests can be run in a github organization
+  # with no billing
+  private = false
+
+  has_issues = true
+  has_wiki = true
+  allow_merge_commit = true
+  allow_squash_merge = false
+  allow_rebase_merge = false
+  has_downloads = true
+  auto_init = true
+  default_branch = "master"
+}
+`, randString, randString)
+}
+
 func testAccGithubRepositoryConfigTemplates(randString string) string {
 	return fmt.Sprintf(`
 resource "github_repository" "foo" {