Add explicit mkpath to Pathname#write_env_script

Library/Homebrew/extend/pathname.rb

@@ -362,6 +362,7 @@ class Pathname
   def write_env_script target, env
     env_export = ''
     env.each {|key, value| env_export += "#{key}=\"#{value}\" "}
+    dirname.mkpath
     self.write <<-EOS.undent
     #!/bin/bash
     #{env_export}exec "#{target}" "$@"