Upgrade errorprone to 2.0.15

Change-Id: I05d3e12178f8f0b5a687c8e09c2dcf80580acfb4
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

pom.xml

@@ -308,7 +308,7 @@
             <dependency>
               <groupId>com.google.errorprone</groupId>
               <artifactId>error_prone_core</artifactId>
-              <version>2.0.14</version>
+              <version>2.0.15</version>
             </dependency>
           </dependencies>
         </plugin>