Update sqlite3 requirement from ~> 1.6.2 to ~> 1.7.0

Updates the requirements on [sqlite3](https://github.com/sparklemotion/sqlite3-ruby) to permit the latest version.
- [Release notes](https://github.com/sparklemotion/sqlite3-ruby/releases)
- [Changelog](https://github.com/sparklemotion/sqlite3-ruby/blob/master/CHANGELOG.md)
- [Commits](sparklemotion/sqlite3-ruby@v1.6.2...v1.7.0)

---
updated-dependencies:
- dependency-name: sqlite3
  dependency-type: direct:development
...

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

mail-notify.gemspec

@@ -33,7 +33,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "rake", "~> 13.0.6"
   spec.add_development_dependency "rspec-rails", "~> 5.1"
   spec.add_development_dependency "standard", "~> 1"
-  spec.add_development_dependency "sqlite3", "~> 1.6.2"
+  spec.add_development_dependency "sqlite3", "~> 1.7.0"
   spec.add_development_dependency "webmock", "~> 3.16.0"
   spec.add_development_dependency "rspec-mocks", "~> 3.12.6"