ruby2.5: replace filter_map with each_with_object

filter_map was introduced in Ruby 2.7, breaking CI on Ruby 2.5 and 2.6.

Author: Erica Windisch

lib/jwt/jwk/set.rb

@@ -22,8 +22,8 @@ def initialize(jwks = nil, options = {}) # rubocop:disable Metrics/CyclomaticCom
                   [jwks]
                 when Hash
                   jwks = jwks.transform_keys(&:to_sym)
-                  [*jwks[:keys]].filter_map do |k|
-                    JWT::JWK.new(k, nil, options)
+                  [*jwks[:keys]].each_with_object([]) do |k, arr|
+                    arr << JWT::JWK.new(k, nil, options)
                   rescue JWT::UnsupportedKeyType
                     nil
                   end