encoding/json: spell "marshaling" and "unmarshaling" consistently

Fixes #12431

Change-Id: I67c42bf2cd9285f471387248fd9c22a16b158349
Reviewed-on: https://go-review.googlesource.com/14150Reviewed-by: Dmitri Shuralyov <shurcool@gmail.com>
Reviewed-by: Rob Pike <r@golang.org>

src/encoding/json/decode.go

@@ -57,7 +57,7 @@ import (
 //
 // If a JSON value is not appropriate for a given target type,
 // or if a JSON number overflows the target type, Unmarshal
-// skips that field and completes the unmarshalling as best it can.
+// skips that field and completes the unmarshaling as best it can.
 // If no more serious errors are encountered, Unmarshal returns
 // an UnmarshalTypeError describing the earliest such error.
 //

src/encoding/json/decode_test.go

@@ -1206,12 +1206,12 @@ func TestStringKind(t *testing.T) {
 
 	data, err := Marshal(m1)
 	if err != nil {
-		t.Errorf("Unexpected error marshalling: %v", err)
+		t.Errorf("Unexpected error marshaling: %v", err)
 	}
 
 	err = Unmarshal(data, &m2)
 	if err != nil {
-		t.Errorf("Unexpected error unmarshalling: %v", err)
+		t.Errorf("Unexpected error unmarshaling: %v", err)
 	}
 
 	if !reflect.DeepEqual(m1, m2) {