Updated the date.
Updated the version number.
Update tree.rb

permit the use of a Proc to render each line of print_tree
example of use:
````
tree.root_node.print_tree 0, method(:print_node)
def print_node(node, prefix)
  # your code
end
````
allow pre 1.9 rubies
Updated the dependencies (gems).
Merged the print_tree improvements.

This will allow an optional block to be added to the print_tree method.

See pull request https://github.com/evolve75/RubyTree/pull/26.

Merge branch 'net1957-master'
Merge branch 'next'
Updated the dependencies (gems) and updated the version.

Merge branch 'next'
Updated the release date for the gem file.
Updated the release date for the gem file.

Merge branch 'next'