Frozen string literal usage unsupported in Ruby 1.9.x

[shiivan]

The latest release v1.3.13 contained this PR change: https://github.com/wvanbergen/chunky_png/pull/147/files#diff-aeb7019729c0cb42388238cf56a1c86146cc275eafa5727205ba81604fc034eeR146

This doesn't appear to work in some of the gems stated supported Ruby versions of 1.9.x

Error in wild:

21:12:20 /var/lib/gems/1.9.1/gems/chunky_png-1.3.13/lib/chunky_png.rb:146:in `<module:ChunkyPNG>': undefined method `b' for "\x00":String (NoMethodError)
21:12:20 	from /var/lib/gems/1.9.1/gems/chunky_png-1.3.13/lib/chunky_png.rb:25:in `<top (required)>'

Simple irb reproduction:

irb(main):001:0> # frozen-string-literal: true
irb(main):002:0* EXTRA_BYTE = "\0".b
NoMethodError: undefined method `b' for "\u0000":String
        from (irb):2
        from /usr/bin/irb:12:in `<main>'

[wvanbergen]

I have updated the wiki to state only currrently supported versions of Ruby (which right now is Ruby 2.5+) are tested against, and supported by ChunkyPNG.

Ruby 1.9 went out of support 5 years ago: https://www.ruby-lang.org/en/news/2015/02/23/support-for-ruby-1-9-3-has-ended/. I do not plan to support it. If you are stuck on Ruby 1.9, pin your ChunkyPNG version on a version that works for you.