Denormalize function defaults to latest version

Minor docs fix

Signed-off-by: Joffrey F <joffrey@docker.com>

compose/config/serialize.py

@@ -35,7 +35,7 @@ def denormalize_config(config):
 
     version = config.version
     if version not in (V2_0, V2_1):
-        version = V2_0
+        version = V2_1
 
     return {
         'version': version,

docs/compose-file.md

@@ -623,7 +623,7 @@ An example:
 
 #### link_local_ips
 
-> [Version 2.1 file format](#version-2.1) only.
+> [Added in version 2.1 file format](#version-21).
 
 Specify a list of link-local IPs. Link-local IPs are special IPs which belong
 to a well known subnet and are purely managed by the operator, usually

tests/acceptance/cli_test.py

@@ -257,7 +257,7 @@ class CLITestCase(DockerClientTestCase):
         self.base_dir = 'tests/fixtures/v1-config'
         result = self.dispatch(['config'])
         assert yaml.load(result.stdout) == {
-            'version': '2.0',
+            'version': '2.1',
             'services': {
                 'net': {
                     'image': 'busybox',