Add mkdir_p to FileUtils.install

[satmandu]

Fixes #103

• PR to solve the aforementioned issue of FileUtils.install not creating a destination directory before installing a file to a destination directory.
• Using mkdir_p on the destination directory solves that issue.

[satmandu]

Is this acceptable @hsbt ?

[hsbt]

Thanks for your work. At least, We need to the additional tests. Can you add them?

[satmandu]

Thanks for your work. At least, We need to the additional tests. Can you add them?

What are the additional needed tests?

[satmandu]

@hsbt What additional tests are needed?

[hsbt]

for your changes.

[satmandu]

Ah! I will modify https://github.com/ruby/fileutils/blob/master/test/fileutils/test_fileutils.rb ...

[satmandu]

Does this work?

[hsbt]

I'll fix this CI fails. It's not related with your tests.

[satmandu]

@hsbt Any chance of this getting merged?