Remove trailing carriage returns from answers (#559)

`comms.Question` removes the tailing '\n' (added when pressing enter),
hence callers expect a result where the result of pressing "enter" when
answering is removed.

However, on Windows, pressing enter adds not only `\n` but `\r\n`, causing
the code that compare the output with a given string work only on unix and
ios. (causing, e.g. #558)

comms/question.go

@@ -22,7 +22,7 @@ func (q Question) Read(r io.Reader) (string, error) {
 	if err != nil {
 		return "", err
 	}
-	s = strings.Trim(s, "\n")
+	s = strings.TrimSpace(s)
 	if s == "" {
 		return q.DefaultValue, nil
 	}

comms/question_test.go

@@ -17,6 +17,9 @@ func TestQuestion(t *testing.T) {
 	}{
 		{"records interactive response", "hello\n", "", "hello"},
 		{"responds with default if response is empty", "\n", "Fine.", "Fine."},
+		{"removes trailing \\r in addition to trailing \\", "hello\r\n", "Fine.", "hello"},
+		{"removes trailing white spaces", "hello  \n", "Fine.", "hello"},
+		{"falls back to default value", "  \n", "Default", "Default"},
 	}
 	for _, test := range tests {
 		q := &Question{