Bugfix: Recognise ERB files correctly in Neovim

These are reported as "eruby", not "erb", so we need to account for
this.

lib/ruby_lsp/server.rb

@@ -296,7 +296,7 @@ def text_document_did_open(message)
       @mutex.synchronize do
         text_document = message.dig(:params, :textDocument)
         language_id = case text_document[:languageId]
-        when "erb"
+        when "erb", "eruby"
           Document::LanguageId::ERB
         else
           Document::LanguageId::Ruby