chore(deps-dev): update rubocop requirement from = 1.6.1 to = 1.7.0 (#294)

Updates the requirements on [rubocop](https://github.com/rubocop-hq/rubocop) to permit the latest version.
- [Release notes](https://github.com/rubocop-hq/rubocop/releases)
- [Changelog](https://github.com/rubocop-hq/rubocop/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop@v1.6.1...v1.7.0)

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

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Author: dependabot-preview[bot]

appium_lib_core.gemspec

@@ -31,7 +31,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'minitest', '~> 5.0'
   spec.add_development_dependency 'minitest-reporters', '~> 1.1'
   spec.add_development_dependency 'webmock', '~> 3.11.0'
-  spec.add_development_dependency 'rubocop', '1.6.1'
+  spec.add_development_dependency 'rubocop', '1.7.0'
   spec.add_development_dependency 'appium_thor', '~> 1.0'
   spec.add_development_dependency 'pry'
   spec.add_development_dependency 'pry-byebug'