Bump assertj-core version to 3.11.1
<properties>
<!-- guava 21+ is for java 8 -->
<guava.version>21.0</guava.version>
- <assertj-core.version>3.9.1</assertj-core.version>
+ <assertj-core.version>3.11.1</assertj-core.version>
</properties>
<dependencies>
