fixed FrozenError error caused by frozen string literal

[taichi-ishitani]

Hi,

I got following FrozenError when I used ruby-ole gem and --enable-frozen-string-literal option.

  FrozenError:
       can't modify frozen String, created at C:/Ruby/Ruby25-x64/lib/ruby/gems/2.5.0/gems/ruby-ole-1.2.12.1/lib/ole/ranges_io.rb:159

This PR is to fix the above error.

[aquasync]

Interesting, didn't know that was a thing. Can you push one without the whitespace changes? I don't like to have behavioural and whitespace/formatting changes in the same commit.

[taichi-ishitani]

Sure, wait a moment.

[taichi-ishitani]

Hi @aquasync ,
I pushed the fix without white space and formatting changes.

[aquasync]

Cool thanks

[aquasync]

While the regular tests work, I can't get RUBYOPT="--enable-frozen-string-literal" rake test to work as it fails in test/unit. I'm using an old ruby 2.3 though so maybe it works fine on newer ones.

[aquasync]

Hmm, if I hack around that I get failures in the tests due to force_encoding on literals in test_filesystem.rb, a simple breakage in test_support.rb, and two strange IOErrors (not open for writing).

[taichi-ishitani]

Hi @aquasync ,
I cleaned up unit test errors caused by frozen string literal and opened a new PR (#24) for this topic.