Examples: Update gRPC version. (#1816)

Author: songy23

examples/build.gradle

@@ -34,7 +34,7 @@ group = "io.opencensus"
 version = "0.20.0-SNAPSHOT" // CURRENT_OPENCENSUS_VERSION
 
 def opencensusVersion = "0.19.2" // LATEST_OPENCENSUS_RELEASE_VERSION
-def grpcVersion = "1.18.0" // CURRENT_GRPC_VERSION
+def grpcVersion = "1.19.0" // CURRENT_GRPC_VERSION
 def prometheusVersion = "0.6.0"
 def jettyVersion = "9.4.12.v20180830"