Replace missing kindlegen.rb repo location with new gist

Author: harlantwood

README.asciidoc

@@ -59,7 +59,7 @@ If you are on OSX and using Homebrew http://mxcl.github.com/homebrew/ you can in
 
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 $ brew install asciidoc source-highlight fop
-$ brew install https://raw.github.com/adamv/homebrew-alt/master/non-free/kindlegen.rb
+$ brew install https://gist.github.com/raw/4064648/kindlegen.rb
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 Initialize a new book with `init`: