Merge pull request #455 from philips/fixup-cas-header

chore(Documentation/api): introduce acronym later in the text

Documentation/api.md

@@ -357,9 +357,9 @@ curl -X GET http://127.0.0.1:4001/v2/keys/dir/asdf\?consistent\=true\&wait\=true
 }
 ```
 
-### Atomic Compare-and-Swap (CAS)
+### Atomic Compare-and-Swap
 
-Etcd can be used as a centralized coordination service in a cluster and `CompareAndSwap` is the most basic operation used to build a distributed lock service.
+Etcd can be used as a centralized coordination service in a cluster and `CompareAndSwap` (CAS) is the most basic operation used to build a distributed lock service.
 
 This command will set the value of a key only if the client-provided conditions are equal to the current conditions.