The Ruby 1.9 hash syntax causes syntax check errors in Sublime Text 2 with a red exclamation mark.

TL;DR

Preferences -> Package Settings -> SublimeLinter -> Settings - User

{
    "sublimelinter_executable_map":
    {
        "ruby": "rvm-auto-ruby"
    }
}

And restart Sublime Text 2

Configuring the SubLime Linter Plugin to use Ruby 1.9 Syntax