chore(gemspec): update fluentd >= 1.14.x

 - update fluentd to 1.14.0 gem

Fluentd changelog for [v1.14.0](https://github.com/fluent/fluentd/blob/master/CHANGELOG.md#v1140)

Signed-off-by: Anton Ouzounov <[email protected]>

Author: Anton Ouzounov

fluent-plugin-google-cloud.gemspec

@@ -10,7 +10,7 @@ eos
   gem.homepage      =
     'https://github.com/GoogleCloudPlatform/fluent-plugin-google-cloud'
   gem.license       = 'Apache-2.0'
-  gem.version       = '0.12.1'
+  gem.version       = '0.13.0'
   gem.authors       = ['Stackdriver Agents Team']
   gem.email         = ['[email protected]']
   gem.required_ruby_version = Gem::Requirement.new('>= 2.2')
@@ -22,7 +22,7 @@ eos
   # Note: In order to update the Fluentd version, please update both here and
   # also the fluentd version in
   # https://github.com/GoogleCloudPlatform/google-fluentd/blob/master/config/software/fluentd.rb.
-  gem.add_runtime_dependency 'fluentd', '1.13.3'
+  gem.add_runtime_dependency 'fluentd', '~> 1.14.0'
   gem.add_runtime_dependency 'googleapis-common-protos', '1.3.10'
   gem.add_runtime_dependency 'googleauth', '0.9.0'
   gem.add_runtime_dependency 'google-api-client', '0.30.8'