Add explicit mkpath to Pathname#write_jar_script

Library/Homebrew/extend/pathname.rb

@@ -380,6 +380,7 @@ class Pathname
 
   # Writes an exec script that invokes a java jar
   def write_jar_script target_jar, script_name, java_opts=""
+    mkpath
     (self+script_name).write <<-EOS.undent
       #!/bin/bash
       exec java #{java_opts} -jar #{target_jar} "$@"