Update nokogiri requirement from ~> 1.13.1 to >= 1.13.1, < 1.16.0 (#110)

Updates the requirements on [nokogiri](https://github.com/sparklemotion/nokogiri) to permit the latest version.
- [Release notes](https://github.com/sparklemotion/nokogiri/releases)
- [Changelog](https://github.com/sparklemotion/nokogiri/blob/main/CHANGELOG.md)
- [Commits](sparklemotion/nokogiri@v1.13.8...v1.15.3)

---
updated-dependencies:
- dependency-name: nokogiri
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Gemfile.lock

@@ -2,18 +2,18 @@ PATH
   remote: .
   specs:
     ofx (0.3.3)
-      nokogiri (~> 1.13.1)
+      nokogiri (>= 1.13.1, < 1.16.0)
 
 GEM
   remote: https://rubygems.org/
   specs:
     byebug (11.1.3)
     diff-lcs (1.5.0)
-    mini_portile2 (2.8.0)
-    nokogiri (1.13.8)
-      mini_portile2 (~> 2.8.0)
+    mini_portile2 (2.8.2)
+    nokogiri (1.15.3)
+      mini_portile2 (~> 2.8.2)
       racc (~> 1.4)
-    racc (1.6.0)
+    racc (1.7.1)
     rake (13.0.6)
     rspec (3.11.0)
       rspec-core (~> 3.11.0)

ofx.gemspec

@@ -24,7 +24,7 @@ Gem::Specification.new do |s|
   s.require_paths = ['lib']
   s.licenses      = ['MIT']
 
-  s.add_dependency 'nokogiri', '~> 1.13.1'
+  s.add_dependency 'nokogiri', '>= 1.13.1', '< 1.16.0'
   s.add_development_dependency 'byebug', '~> 11.1.3'
   s.add_development_dependency 'rake', '~> 13.0.6'
   s.add_development_dependency 'rspec', '~> 3.10'