Added support for replicas keys in v3

resolves #644 `replicas` key

script/test/fixtures/v3/output-k8s-full-example.json

@@ -160,7 +160,7 @@
         }
       },
       "spec": {
-        "replicas": 1,
+        "replicas": 6,
         "template": {
           "metadata": {
             "creationTimestamp": null,

script/test/fixtures/v3/output-os-full-example.json

@@ -182,7 +182,7 @@
             }
           }
         ],
-        "replicas": 1,
+        "replicas": 6,
         "test": false,
         "selector": {
           "io.kompose.service": "foo"