Update simplecov requirement from ~> 0.15 to ~> 1.0

Updates the requirements on [simplecov](https://github.com/simplecov-ruby/simplecov) to permit the latest version.
- [Release notes](https://github.com/simplecov-ruby/simplecov/releases)
- [Changelog](https://github.com/simplecov-ruby/simplecov/blob/main/CHANGELOG.md)
- [Commits](simplecov-ruby/simplecov@v0.15.0...v1.0.0)

---
updated-dependencies:
- dependency-name: simplecov
  dependency-version: 1.0.0
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

split.gemspec

@@ -39,7 +39,7 @@ Gem::Specification.new do |s|
   s.add_dependency "cgi"
 
   s.add_development_dependency "bundler",     ">= 1.17"
-  s.add_development_dependency "simplecov",   "~> 0.15"
+  s.add_development_dependency "simplecov",   "~> 1.0"
   s.add_development_dependency "rack-test",   "~> 2.0"
   s.add_development_dependency "rake",        "~> 13"
   s.add_development_dependency "rspec",       "~> 3.7"