Add Path::Tiny to required
replace use of File::Slurp with Path::Tiny

This change moves from File::Slurp to Path::Tiny.
File::Slurp is known to be buggy and vulnerable.
See also:

https://rt.cpan.org/Public/Bug/Display.html?id=95484
Merge pull request #8 from MartinMcGrath/master

Move from using File::Slurp to Path::Tiny