Formula#install has public visibility

It is called with an explicit receiver in build.rb, so the base class
method should also be public.

Library/Homebrew/formula.rb

@@ -576,11 +576,11 @@ class Formula
     HOMEBREW_LIBRARY.join("Homebrew", "test", "fixtures", file)
   end
 
-  protected
-
   def install
   end
 
+  protected
+
   # Pretty titles the command and buffers stdout/stderr
   # Throws if there's an error
   def system cmd, *args