goprotobuf: Fix test for text format number too large for int64.

LGTM=nigeltao
R=nigeltao
CC=golang-codereviews
https://codereview.appspot.com/111460043
diff --git a/proto/text_parser_test.go b/proto/text_parser_test.go
index e447ffa..d043769 100644
--- a/proto/text_parser_test.go
+++ b/proto/text_parser_test.go
@@ -156,8 +156,8 @@
 
 	// Number too large for int64
 	{
-		in:  "count: 123456789012345678901",
-		err: "line 1.7: invalid int32: 123456789012345678901",
+		in:  "count: 1 others { key: 123456789012345678901 }",
+		err: "line 1.23: invalid int64: 123456789012345678901",
 	},
 
 	// Number too large for int32