Upgrade error_prone_core to 2.0.18

Change-Id: Ide6cecf32cc0b4b36593607fc8302cec54ef5c08

pom.xml

diff --git a/pom.xml b/pom.xml
index f7246c7..b28af42 100644
--- a/pom.xml
+++ b/pom.xml
@@ -395,7 +395,7 @@
           <dependency>
             <groupId>com.google.errorprone</groupId>
             <artifactId>error_prone_core</artifactId>
-            <version>2.0.15</version>
+            <version>2.0.18</version>
           </dependency>
         </dependencies>
       </plugin>