MAGETWO-93674: Add pcntl to composer dependency

Author: duhon

composer.json

@@ -81,6 +81,9 @@
         "lusitanian/oauth": "~0.8.10",
         "sebastian/phpcpd": "2.0.4"
     },
+    "suggest": {
+        "ext-pcntl": "Need for parallel indexing"
+    },
     "replace": {
         "magento/module-marketplace": "100.2.2",
         "magento/module-admin-notification": "100.2.3",