Merge pull request #12 from tedkulp/master

Add option to pass environment along to knife bootstrap
added gem version badge
ensure status of image details is OK before outputting image name
Merge pull request #19 from salemine/fix-name-error

Exception: NoMethodError: undefined method `name' for nil:NilClass - ensure status of image details is OK before outputting image name
ignore ruby-head travis result
… but still run on ruby-head…
bump dependency
prepare release
updated changelog
remove guard as it is now 1.9+ only