Creating the build directory when building linux local

The build currently happens on wkhtmltopdf/static-build/linux-local, however the packer expects it to happen on wkhtmltopdf/static-build/linux-local/build as consequences builds for linux-local are failing right now.

All the others builds happens on the `build` directory too.
Merge pull request #25 from renan/patch-1

Creating the build directory when building linux local