Allow tilde in zip entry names

[jdleesmiller]

Use absolute_path rather than expand_path to allow tilde to pass through unchanged. Otherwise, we try to expand it to a home directory.

For example, a zip containing a file named ~tilde~ caused this error on extraction:

  1) Error:
PathTraversalTest#test_entry_name_with_tilde:
ArgumentError: user tilde~ doesn't exist
    /Users/john/ex/rubyzip/lib/zip/entry.rb:120:in `expand_path'

because it interpreted ~tilde~ as "get me the path to the home directory of the user tilde~.

An entry name containing ~ should still be considered 'safe', provided that the user doesn't use it in a shell context where the ~ would again be expanded.

This was introduced in #376 .

Thanks to @mmazour for catching this.

[coveralls]

Coverage increased (+4.08%) to 99.836% when pulling ad15c3c on jdleesmiller:fix-expand-path into 8ece5c9 on rubyzip:master.