Install psalm as dev, sync scripts updates

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

@@ -0,0 +1,26 @@
+<?php
+
+namespace LanguageServerProtocol;
+
+abstract class DiagnosticSeverity
+{
+    /**
+     * Reports an error.
+     */
+    const ERROR = 1;
+
+    /**
+     * Reports a warning.
+     */
+    const WARNING = 2;
+
+    /**
+     * Reports an information.
+     */
+    const INFORMATION = 3;
+
+    /**
+     * Reports a hint.
+     */
+    const HINT = 4;
+}