Enable warnings in error-prone compilation

Change-Id: Ibda5a29a8b37bc8d9da3b683afbcfcfb2432cd89

pom.xml

diff --git a/pom.xml b/pom.xml
index 28ed991..f3c0622 100644
--- a/pom.xml
+++ b/pom.xml
@@ -385,6 +385,10 @@
         <configuration>
           <compilerId>javac-with-errorprone</compilerId>
           <forceJavacCompilerUse>true</forceJavacCompilerUse>
+          <showWarnings>true</showWarnings>
+          <compilerArgs>
+            <arg>-Xlint:deprecation</arg>
+          </compilerArgs>
           <source>${java.version}</source>
           <target>${java.version}</target>
           <encoding>UTF-8</encoding>