[rb] Fix credential issue with private key

rb/lib/selenium/webdriver/common/virtual_authenticator/credential.rb

@@ -47,7 +47,7 @@ def from_json(opts)
           new(id: decode(opts['credentialId']),
               resident_credential: opts['isResidentCredential'],
               rp_id: opts['rpId'],
-              private_key: opts['privateKey'],
+              private_key: decode(opts['privateKey']),
               sign_count: opts['signCount'],
               user_handle: user_handle)
         end

rb/spec/unit/selenium/webdriver/common/credentials_spec.rb

@@ -95,7 +95,7 @@ module WebDriver
           expect(credential.resident_credential?).to be(true)
           expect(credential.rp_id).to eq('localhost')
           expect(credential.user_handle).to eq(user_handle)
-          expect(credential.private_key).to eq(base64_encoded_pk)
+          expect(credential.private_key).to eq(described_class.decode(base64_encoded_pk))
           expect(credential.sign_count).to eq(0)
         end
       end