Fail when run without -t

[Igor Zubkov]

$ bundle show | grep mry
  * mry (0.48.1.1)
$ bundle exec mry
Usage: mry [options] [.rubocop.yml]
    -t, --target=TARGET_VERSION
$ bundle exec mry .rubocop.yml 
bundler: failed to load command: mry (/Users/biow0lf/.rbenv/versions/2.4.1/bin/mry)
NoMethodError: undefined method `>=' for nil:NilClass
  /Users/biow0lf/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/mry-0.48.1.1/lib/mry/runner.rb:16:in `block in run'
  /Users/biow0lf/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/mry-0.48.1.1/lib/mry/runner.rb:16:in `select'
  /Users/biow0lf/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/mry-0.48.1.1/lib/mry/runner.rb:16:in `run'
  /Users/biow0lf/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/mry-0.48.1.1/lib/mry/cli.rb:12:in `run'
  /Users/biow0lf/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/mry-0.48.1.1/exe/mry:5:in `<top (required)>'
  /Users/biow0lf/.rbenv/versions/2.4.1/bin/mry:22:in `load'
  /Users/biow0lf/.rbenv/versions/2.4.1/bin/mry:22:in `<top (required)>'
$ bundle exec mry -t 0.48.1 .rubocop.yml 
$ 

[Masataka Pocke Kuwabara]

Thanks for your bug report!
I've fixed the bug in #8 , and released v0.48.1.2 .
https://github.com/pocke/mry/releases/tag/v0.48.1.2