Bumped version of gRPC to 1.3.1

Change-Id: I7798476bd443a796e0e6a6e149ab8f66435ba4fa
diff --git a/lib/pom.xml b/lib/pom.xml
index d53b2c7..7b8f528 100644
--- a/lib/pom.xml
+++ b/lib/pom.xml
@@ -54,7 +54,7 @@
                   to fix locale errors for non-US developers. However, it breaks
                   SonarQube's test coverage, so moving here for now. -->
         <argLine>-Duser.language=en -Duser.region=US</argLine>
-        <grpccore.version>1.3.0</grpccore.version>
+        <grpccore.version>1.3.1</grpccore.version>
     </properties>
 
     <dependencyManagement>