Auto merge of servo#10332 - zofrex:patch-1, r=frewsxcv

Change OS X 10.11 to El Capitan

I think "El Capitan" is a lot clearer than 10.11 – I had to look up which version that was. Thoughts?

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Author: bors-servo

README.md

@@ -25,7 +25,7 @@ On OS X (MacPorts):
 sudo port install python27 py27-virtualenv cmake
 ```
 
-On OS X 10.11, you also have to install openssl:
+On OS X 10.11 (El Capitan), you also have to install openssl:
 
 ``` sh
 brew install openssl