Fix frozen string issues

[st0012]

This PR:

• Adds a test suite for Ruby option --enable-frozen-string-literal
• Fixes can't modify frozen String on Rails 5.2 and Ruby 2.7 #967
• Make tests runnable under --enable-frozen-string-literal option

[codecov-commenter]

Codecov Report

Merging #977 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #977   +/-   ##
=======================================
  Coverage   97.35%   97.35%           
=======================================
  Files          46       46           
  Lines        2081     2081           
=======================================
  Hits         2026     2026           
  Misses         55       55           

Impacted Files	Coverage Δ
spec/raven/event_spec.rb	97.55% <ø> (ø)
spec/raven/processors/utf8conversion_spec.rb	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c51215f...687394c. Read the comment docs.

[myronmarston]

Thanks for fixing this @st0012. We ran into this when we tried to add sentry to a project that is using the --enable-frozen-string-literal option. When do you expect to cut a release that includes this?

[myronmarston]

BTW, I noticed there's a 3.0.1 milestone with a ton of issues assigned to it. Any chance you can cut a release with just this fix before getting all those issues fixed? We basically can't use the gem at all until this is fixed.

[st0012]

@myronmarston I'm the new maintainer of this gem and I'm still triaging all the issues and that's why most of them are all in the same milestone. But after most of them are categorized I will move them into different ones and 3.0.1 should be released before next weekend.

[myronmarston]

Sounds good, thanks :).