POM: Add --should-stop=ifError=FLOW to javac flags.

Error Prone demands this now.

Change-Id: I1640daec54026aa4ea36be7f9cc81c9ff03f6b77
diff --git a/jgvariant-parent/pom.xml b/jgvariant-parent/pom.xml
index 834296e..d543624 100644
--- a/jgvariant-parent/pom.xml
+++ b/jgvariant-parent/pom.xml
@@ -219,6 +219,7 @@
               <arg>-J--add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED</arg>
               <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED</arg>
               <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED</arg>
+              <arg>--should-stop=ifError=FLOW</arg>
             </compilerArgs>
             <annotationProcessorPaths>
               <path>