message: Use ByteArrayOutputStream.toString(string) instead of toString(charset).
  Maintains compatibility with JDK8 and fixes continuous testing failure.
diff: package com.google.crypto.tink.testing;
  -import static java.nio.charset.StandardCharsets.UTF_8;
  -
  import com.google.crypto.tink.Aead;
  import com.google.crypto.tink.BinaryKeysetReader;
  import com.google.crypto.tink.BinaryKeysetWriter;
  @@ -143,7 +141,7 @@ public final class KeysetServiceImpl extends KeysetImplBase {
  JsonKeysetWriter.withOutputStream(jsonKeysetStream).write(keyset);
  jsonKeysetStream.close();
  response =
  - KeysetToJsonResponse.newBuilder().setJsonKeyset(jsonKeysetStream.toString(UTF_8)).build();
  + KeysetToJsonResponse.newBuilder().setJsonKeyset(jsonKeysetStream.toString("UTF-8")).build();
  } catch (GeneralSecurityException | InvalidProtocolBufferException e) {
  response = KeysetToJsonResponse.newBuilder().setErr(e.toString()).build();
  } catch (IOException e) {
  