Removed Python ':' remnants that caused the Ruby gem to fail.

Upon requiring the Gem (`require 'dstk'`) I would get this error:

    SyntaxError: /Users/campeterson/.rvm/gems/ruby-1.9.3-p392/gems/dstk-0.50.1/lib/dstk.rb:31: syntax error, unexpected ':', expecting keyword_then or ';' or '\n'
    /Users/campeterson/.rvm/gems/ruby-1.9.3-p392/gems/dstk-0.50.1/lib/dstk.rb:84: syntax error, unexpected tLABEL
    /Users/campeterson/.rvm/gems/ruby-1.9.3-p392/gems/dstk-0.50.1/lib/dstk.rb:157: syntax error, unexpected keyword_end, expecting $end
    from /Users/campeterson/.rvm/rubies/ruby-1.9.3-p392/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:60:in `require'

Turned out to be a couple of `:` that may have been left over from the conversion from Python.