fix #1711 elasticsearch 6.3

dbflute.xml

plugin.xml

pom.xml

src/main/java/org/codelibs/fess/api/es/EsApiManager.java

src/main/java/org/codelibs/fess/api/json/JsonApiManager.java

...codelibs/fess/app/web/admin/backup/AdminBackupAction.java

...g/codelibs/fess/app/web/admin/esreq/AdminEsreqAction.java

...s/fess/app/web/api/admin/backup/ApiAdminBackupAction.java

src/main/java/org/codelibs/fess/dict/DictionaryManager.java

src/main/java/org/codelibs/fess/entity/PingResponse.java

src/main/java/org/codelibs/fess/es/client/FessEsClient.java

src/main/java/org/codelibs/fess/helper/CurlHelper.java

...ain/java/org/codelibs/fess/timer/SystemMonitorTarget.java

src/main/java/org/codelibs/fess/util/UpgradeUtil.java

.../java/org/codelibs/fess/helper/AccessTokenHelperTest.java

src/test/java/org/codelibs/fess/helper/QueryHelperTest.java

...test/java/org/codelibs/fess/it/admin/SearchListTests.java

src/test/java/org/codelibs/fess/util/DocMapTest.java

...test/java/org/codelibs/fess/util/KuromojiCSVUtilTest.java