Bump version to 0.30 (#143)

Author: bshaffer

src/ApiCore/AgentHeaderDescriptor.php

@@ -40,7 +40,7 @@ class AgentHeaderDescriptor
     const AGENT_HEADER_KEY = 'x-goog-api-client';
     // TODO(michaelbausor): include bumping this version in a streamlined
     // release process. Issue: https://github.com/googleapis/gax-php/issues/48
-    const API_CORE_VERSION = '0.29.0';
+    const API_CORE_VERSION = '0.30.0';
     const UNKNOWN_VERSION = '';
 
     private $metricsHeaders;