Chef 11 requires

    node.default['drush']['version'] = release.text('v')

or it thinks attributes are read-only
Merge pull request #17 from theodi/master

Explicitly uses default precedence level for node attr writes.
Added redhat to the list of supported platforms
Merge pull request #18 from u2illc/master

Adds redhat support.
add conditionals to only upgrade / install drush if not yet installed (pear install takes too long for repeat installs)