Completion Request should return CompletionList

As discussed in
microsoft/language-server-protocol#39
statically typed languages like Java do not support mixed return types,
which in the case of Completion Request is `CompletionItem[] |
CompletionList`.

Thus Typefox - the Java client of the language server protocol - accepts
only `CompletionList`, which contains `CompletionItem[]`.

In order to work with Eclipse Che and other IDEs using the Typefox
client, the Completion Request handler in the PHP language server should
return `CompletionList` instead of `CompletionItems[]`.

src/Server/TextDocument.php

@@ -17,7 +17,8 @@
     FormattingOptions,
     TextEdit,
     CompletionItem,
-    CompletionItemKind
+    CompletionItemKind,
+    CompletionList
 };
 use LanguageServer\Server\Completion\PHPKeywords;
 
@@ -166,17 +167,19 @@ public function formatting(TextDocumentIdentifier $textDocument, FormattingOptio
 
     public function completion(TextDocumentIdentifier $textDocument, Position $position)
     {
-        $items = [];
+        $list = new CompletionList();
+        $list->isIncomplete = false;
+        $list->items = [];
         $keywords = new PHPKeywords();
         foreach ($keywords->getKeywords() as $keyword){
             $item = new CompletionItem();
             $item->label = $keyword->getLabel();
             $item->kind = CompletionItemKind::KEYWORD;
             $item->insertText = $keyword->getInsertText();
             $item->detail = "PHP Language Server";
-            $items[] = $item;
+            $list->items[] = $item;
         }
-        return $items;
+        return $list;
     }
 
 }