Fixed an old reference to puma

doc/install/installation.md

@@ -185,7 +185,7 @@ You can change `5-3-stable` to `master` if you want the *bleeding edge* version,
     sudo -u git -H mkdir public/uploads
     sudo chmod -R u+rwX  public/uploads
-    # Copy the example Puma config
+    # Copy the example Unicorn config
     sudo -u git -H cp config/unicorn.rb.example config/unicorn.rb
     # Enable cluster mode if you expect to have a high load instance