bump LSP4J version 0.14.0 to 0.20.1

[w6et]

LSP4J 0.20.1 has now been released
lemminx now just use 0.14.0，i suggest bump the version 0.14.0 to 0.20.1
benefit：

• some bugfix from 0.14.0 to 0.20.1
• lsp4j runtime base on java8(compatible)

code change:
org.eclipse.lemminx.XMLTextDocumentService#prepareRename

Either<Range, PrepareRenameResult> either = getXMLLanguageService().prepareRename(xmlDocument, params.getPosition(), cancelChecker);
if (either != null) {
	if(either.isLeft()) {
		return Either3.forFirst((Range)either.get());
	}else {
		return Either3.forSecond((PrepareRenameResult)either.get());
	}
}else {
	return null;
}
//return getXMLLanguageService().prepareRename3(xmlDocument, params.getPosition(), cancelChecker);

#在 LSP4J 0.15.0
Return type of textDocument/prepareRename changed from Either<Range, PrepareRenameResult>
to Either3<Range, PrepareRenameResult, PrepareRenameDefaultBehavior>

[angelozerr]

@w6et is there any chance that you create a PR?

[w6et]

@w6et is there any chance that you create a PR?

/eclipse/lemminx/pull/1498

[datho7561]

Closed in #1498