Upgrade error_prone_core to 2.1.1

And maven-compiler-plugin to 3.6.2

Change-Id: I0c010a75c58391173908faf9ced4346aed7672fd

pom.xml

diff --git a/pom.xml b/pom.xml
index 8737499..305f4ef 100644
--- a/pom.xml
+++ b/pom.xml
@@ -380,7 +380,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-compiler-plugin</artifactId>
-        <version>3.6.1</version>
+        <version>3.6.2</version>
         <configuration>
           <compilerId>javac-with-errorprone</compilerId>
           <forceJavacCompilerUse>true</forceJavacCompilerUse>
@@ -399,7 +399,7 @@
           <dependency>
             <groupId>com.google.errorprone</groupId>
             <artifactId>error_prone_core</artifactId>
-            <version>2.0.21</version>
+            <version>2.1.1</version>
           </dependency>
         </dependencies>
       </plugin>