match rubocop diagnostic severities (#1106)

Matched the severities from `lib/rubocop/lsp/severity.rb`, except for leaving `refactor` at the `INFORMATION` severity level, `refactor` violations will return a non-zero exit code/cause CI to fail.

Author: maxnotarangelo

lib/ruby_lsp/requests/support/rubocop_diagnostic.rb

@@ -9,9 +9,9 @@ class RuboCopDiagnostic
 
         RUBOCOP_TO_LSP_SEVERITY = T.let(
           {
-            convention: Constant::DiagnosticSeverity::INFORMATION,
-            info: Constant::DiagnosticSeverity::INFORMATION,
+            info: Constant::DiagnosticSeverity::HINT,
             refactor: Constant::DiagnosticSeverity::INFORMATION,
+            convention: Constant::DiagnosticSeverity::INFORMATION,
             warning: Constant::DiagnosticSeverity::WARNING,
             error: Constant::DiagnosticSeverity::ERROR,
             fatal: Constant::DiagnosticSeverity::ERROR,