add "case '\n'" for ENTER key input.

Because in some keyboard ENTER key value is '\n', so we must add this
value for ENTER key triggled.

Signed-off-by: Shaojie Sun <shaojie.sun@linaro.com>
diff --git a/display.c b/display.c
index e9f4bf6..41a511d 100644
--- a/display.c
+++ b/display.c
@@ -401,6 +401,7 @@
 		display_prev_line();
 		break;
 
+	case '\n':
 	case '\r':
 		display_select();
 		break;
@@ -474,6 +475,7 @@
 
 		break;
 
+	case '\n':
 	case '\r':
 		if (!windata[current_win].ops || !windata[current_win].ops->selectf)
 			return 0;