[CVE-2017-17042] update vulnerable yard dependency

Signed-off-by: Ben Abrams <me@benabrams.it>

Author: majormoses

CHANGELOG.md

@@ -5,6 +5,9 @@ This CHANGELOG follows the format listed [here](https://github.com/sensu-plugins
 
 ## [Unreleased]
 
+### Security
+- updated yard dependency to `~> 0.9.11` per: https://nvd.nist.gov/vuln/detail/CVE-2017-17042 (@majormoses)
+
 ## [2.0.0] - 2018-03-07
 ### Security
 - updated rubocop dependency to `~> 0.51.0` per: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-8418. (@majormoses)

sensu-plugins-cpu-checks.gemspec

@@ -43,5 +43,5 @@ Gem::Specification.new do |s| # rubocop:disable Metrics/BlockLength
   s.add_development_dependency 'redcarpet',                 '~> 3.2'
   s.add_development_dependency 'rspec',                     '~> 3.4'
   s.add_development_dependency 'rubocop',                   '~> 0.51.0'
-  s.add_development_dependency 'yard',                      '~> 0.8'
+  s.add_development_dependency 'yard',                      '~> 0.9.11'
 end