Fatal error

After the last update:
For now I had to disable the plugin.

Fatal error: Uncaught Error: Undefined class constant 'MAJOR_VERSION' in cloudwaysapps.com/gsvszpjvap/public_html/wp-content/plugins/pixel-caffeine/vendor/guzzlehttp/guzzle/src/Utils.php:118

Stack Trace
1.	
GuzzleHttp\Utils::defaultUserAgent()
cloudwaysapps.com/gsvszpjvap/public_html/wp-content/plugins/pixel-caffeine/vendor/guzzlehttp/guzzle/src/functions.php:71
2.	
GuzzleHttp\default_user_agent()
cloudwaysapps.com/gsvszpjvap/public_html/wp-content/plugins/post-smtp/Postman/Postman-Mail/google-api-client/vendor/guzzlehttp/guzzle/src/Client.php:194
3.	
GuzzleHttp\Client->configureDefaults(Array)
cloudwaysapps.com/gsvszpjvap/public_html/wp-content/plugins/post-smtp/Postman/Postman-Mail/google-api-client/vendor/guzzlehttp/guzzle/src/Client.php:75
4.	
GuzzleHttp\Client->__construct(Array)
cloudwaysapps.com/gsvszpjvap/public_html/wp-content/plugins/post-smtp/Postman/Postman-Mail/google-api-client/vendor/google/apiclient/src/Google/Client.php:1058
5.	
/home/29 in cloudwaysapps.com/gsvszpjvap/public_html/wp-content/plugins/pixel-caffeine/vendor/guzzlehttp/guzzle/src/Utils.php on line 118