Bing Ads API V12- Parse error: syntax error, unexpected '.', expecting ',' or ';'

Question

I am using Bing Ads API V12 for php to do some Ads service related operations. The script I am using to get bing ads cost on daily basis with scheduler. Everything works fine when I try it with php v7.0 but If I try it with php v5.6.30 it is causing parse error on line 53 of AuthHelper.php

Parse error: syntax error, unexpected '.', expecting ',' or ';' on line 53

The main library block on line 53 AuthHelper.php is like this on the final class with other const

const CampaignTypes = 
    CampaignType::Audience . ' ' . 
    CampaignType::Search . ' ' . 
    CampaignType::Shopping . ' ' . 
    CampaignType::DynamicSearchAds;

Full ref. of AuthHelper class

https://github.com/BingAds/BingAds-PHP-SDK/blob/master/samples/V12/AuthHelper.php

Possible duplicate: Parse error: syntax error, unexpected '.', expecting ',' or ';'

So my question is how could I fix it now? Should I wrap it with constructor ? Or anything else quick fix?