Install psalm as dev, sync scripts updates

vendor/felixfbecker/language-server-protocol/src/MarkupKind.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace LanguageServerProtocol;
+
+/**
+ * Describes the content type that a client supports in various
+ * result literals like `Hover`, `ParameterInfo` or `CompletionItem`.
+ *
+ * Please note that `MarkupKinds` must not start with a `$`. This kinds
+ * are reserved for internal usage.
+ */
+abstract class MarkupKind
+{
+    /**
+     * Plain text is supported as a content format
+     */
+    const PLAINTEXT = 'plaintext';
+
+    /**
+     * Markdown is supported as a content format
+     */
+    const MARKDOWN = 'markdown';
+}