fix(ci): freeze xdebug version to 3.1.6 which also supports PHP 7.2 (#135)

For more info see https://pecl.php.net/package-changelog.php?package=xdebug&release=3.2.0

Author: bednar

.circleci/config.yml

@@ -51,7 +51,7 @@ commands:
       - run:
           name: Install xdebug
           command: |
-            sudo pecl install xdebug
+            sudo pecl install xdebug-3.1.6
       - run:
           name: Run tests
           command: |