chore(deps): update dependency com.atlassian.commonmark:commonmark-ext-gfm-strikethrough to v0.15.0 (GoogleCloudPlatform#2955)

Author: renovate-bot

run/markdown-preview/renderer/pom.xml

@@ -60,7 +60,7 @@
  <dependency>
  <groupId>com.atlassian.commonmark</groupId>
  <artifactId>commonmark-ext-gfm-strikethrough</artifactId>
- <version>0.14.0</version>
+ <version>0.15.0</version>
  </dependency>
  <dependency>
  <groupId>com.googlecode.owasp-java-html-sanitizer</groupId>