all: trivial formatting changes

Changes:
* import grouping for third-party dependencies
* import grouping for generated protobufs
* blank space removal

Change-Id: I2950b0606bb2064046d79a23a78b05c23147cbfe
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/221017
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/proto/encode_test.go b/proto/encode_test.go
index edef139..80e8f5d 100644
--- a/proto/encode_test.go
+++ b/proto/encode_test.go
@@ -12,6 +12,7 @@
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
+
 	"google.golang.org/protobuf/encoding/prototext"
 	"google.golang.org/protobuf/internal/encoding/wire"
 	"google.golang.org/protobuf/proto"