encoding/jsonpb: change MarshalOptions.Compact option to Indent

This makes it consistent with jsonpb.MarshalOptions. This does change
the default to be in compact form.

Change-Id: I1b07f06f282c019b30f3f1cbb43f6c8cba18f385
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/168405
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
diff --git a/internal/impl/export.go b/internal/impl/export.go
index 12ce51b..801457b 100644
--- a/internal/impl/export.go
+++ b/internal/impl/export.go
@@ -91,6 +91,6 @@
 // MessageStringOf returns the message value as a string,
 // which is the message serialized in the protobuf text format.
 func (Export) MessageStringOf(m pref.ProtoMessage) string {
-	b, _ := textpb.MarshalOptions{Compact: true}.Marshal(m)
+	b, _ := textpb.Marshal(m)
 	return string(b)
 }