Remove strscan dependency declaration from gemspec

[Bo98]

See discussion in #140. strscan is a part of the Ruby standard library in all versions of Ruby supported by REXML.

Fixes #140.

[kou]

Thanks.

The Document CI failure is unrelated.

[hachi8833]

Thank you for the fix!
Hope you released the fixed version of rexml soon.

---

I got the following error on GitHub CI's bundle install, which seems to come from this issue.

Downloading rexml-3.3.6 revealed dependencies not in the API or the lockfile
(strscan (>= 0)).
Running `bundle update rexml` should fix the problem.
Error: The process '/opt/hostedtoolcache/Ruby/3.3.5/x64/bin/bundle' failed with exit code 34

I did a workaround by adding gem 'rexml', github: "ruby/rexml" to Gemfile for now.
I expect this workaround will be unnecessary when the fixed version of rexml is released.

[kou]

We need to fix the CI failure before we release a new version.
Could you try it?

[Bo98]

Unfortunately, it's a Ruby bug it seems: https://bugs.ruby-lang.org/issues/20713.

We can workaround it though I think: #205

[kou]

Thanks for taking a look at this.
I thought that nobody is working on this. So I've done by myself...

[kou]

Released.