Tolerate git config color settings

The commit log and git branch parsing was not working when my commands
were getting colorized.  Explicitly pass --no-color to these two
commands to turn off colors.

commit-id:206a4539

github/githubclient/client.go

@@ -611,7 +611,7 @@ func (c *client) ClosePullRequest(ctx context.Context, pr *github.PullRequest) {
 
 func getLocalBranchName(gitcmd git.GitInterface) string {
 	var output string
-	err := gitcmd.Git("branch", &output)
+	err := gitcmd.Git("branch --no-color", &output)
 	check(err)
 	lines := strings.Split(output, "\n")
 	for _, line := range lines {

spr/spr.go

@@ -303,7 +303,7 @@ func (sd *stackediff) ProfilingSummary() {
 // getLocalCommitStack returns a list of unmerged commits
 func (sd *stackediff) getLocalCommitStack() []git.Commit {
 	var commitLog string
-	logCommand := fmt.Sprintf("log %s/%s..HEAD",
+	logCommand := fmt.Sprintf("log --no-color %s/%s..HEAD",
 		sd.config.Repo.GitHubRemote, sd.config.Repo.GitHubBranch)
 	sd.mustgit(logCommand, &commitLog)
 	commits, valid := sd.parseLocalCommitStack(commitLog)