Fix blacklist bug

See https://github.com/bf4/gemproject/pull/10 and https://twitter.com/hazula/status/396334305313431553


```ruby
list = ["jordansissel\n", "iconara\n", "michaelklishin\n", "atech\n", "adamcooke\n", "niftyware\n"].map(&:strip)
wrong_regexes = list.map{|username| /#{username}/io }
  # =>  [/jordansissel/i, /jordansissel/i, /jordansissel/i, /jordansissel/i, /jordansissel/i, /jordansissel/i]
correct_regexes = list.map{|username| /#{username}/i }
  # =>  [/jordansissel/i, /iconara/i, /michaelklishin/i, /atech/i, /adamcooke/i, /niftyware/i]
```

The `o` flag caused the regex to compile only once, which ignored the other blacklisted usernames