backing out guava upgrade

Author: Matt Darwin

java/pom.xml

@@ -31,7 +31,7 @@
  <target.gen.source.path>${project.basedir}/target/generated-sources</target.gen.source.path>
  <dep.junit.version>4.11</dep.junit.version>
  <dep.slf4j.version>1.7.25</dep.slf4j.version>
- <dep.guava.version>20.0</dep.guava.version>
+ <dep.guava.version>18.0</dep.guava.version>
  <forkCount>2</forkCount>
  <jackson.version>2.7.1</jackson.version>
  <!--<hadoop.version>2.7.1</hadoop.version>-->