Use keyword argument like ERB.new(str, trim_mode: ...) instead

[wata]

Fix #229

I fixed these two warnings

• Passing safe_level with the 2nd argument of ERB.new is deprecated. Do not use it, and specify other arguments as keyword arguments.
• Passing trim_mode with the 3rd argument of ERB.new is deprecated. Use keyword argument like ERB.new(str, trim_mode: ...) instead.

[orta]

It's been a long time since I've written Ruby, can you just clarify that this syntax doesn't affect backwards compatability?

[orta]

well, lets just see how it goes then