#2295 Send an empty object for the initialized notification, per the spec

autoload/ale/lsp/message.vim

@@ -41,7 +41,7 @@ function! ale#lsp#message#Initialize(root_path, initialization_options) abort
 endfunction
 
 function! ale#lsp#message#Initialized() abort
-    return [1, 'initialized']
+    return [1, 'initialized', {}]
 endfunction
 
 function! ale#lsp#message#Shutdown() abort