Use ensure block for File.unlink tempfile (#342)

This ensures that temporary files are removed even if the begin block
fails. This has been happening on some dev machines.

lib/solargraph/language_server/message/text_document/formatting.rb

@@ -26,10 +26,10 @@ def process
               store = RuboCop::ConfigStore.new
               redirect_stdout { RuboCop::Runner.new(options, store).run(paths) }
               result = File.read(tempfile)
-              File.unlink tempfile
               format original, result
             rescue RuboCop::ValidationError, RuboCop::ConfigNotFoundError => e
               set_error(Solargraph::LanguageServer::ErrorCodes::INTERNAL_ERROR, "[#{e.class}] #{e.message}")
+            ensure
               File.unlink tempfile
             end
           end