Keep config keys in alphabetised order

Signed-off-by: Mazz Mosley <[email protected]>

compose/config.py

@@ -24,7 +24,6 @@ DOCKER_CONFIG_KEYS = [
     'env_file',
     'environment',
     'extra_hosts',
-    'read_only',
     'hostname',
     'image',
     'labels',
@@ -37,6 +36,7 @@ DOCKER_CONFIG_KEYS = [
     'pid',
     'ports',
     'privileged',
+    'read_only',
     'restart',
     'security_opt',
     'stdin_open',