v1.12.0: fixed date in CHANGELOG to be in YYYY-MM-DD form

Signed-off-by: Tibor Vass <tibor@docker.com>

CHANGELOG.md

@@ -5,7 +5,7 @@ information on the list of deprecated flags and APIs please have a look at
 https://docs.docker.com/engine/deprecated/ where target removal dates can also
 be found.
 
-## 1.12.0 (07-14-2016)
+## 1.12.0 (2016-07-14)
 
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