Bump grpc-java to 1.18.0

Requires bumping other dependencies in deps.json such as Netty (4.1.32)
and error_prone_annotations. Includes also fixes detected by updated
errorprone.

Change-Id: Ic2bd86931cc89bfb2cf1a4cb11a4586bc8cac608
diff --git a/WORKSPACE b/WORKSPACE
index 8fd6f8d..6d49746 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -41,10 +41,12 @@
 grpc_java_repositories(
     omit_com_google_api_grpc_google_common_protos = True,
     omit_com_google_auth_google_auth_library_credentials = True,
+    omit_com_google_auth_google_auth_library_oauth2_http = True,
     omit_com_google_code_findbugs_jsr305 = True,
     omit_com_google_code_gson = True,
     omit_com_google_errorprone_error_prone_annotations = True,
     omit_com_google_guava = True,
+    omit_com_google_j2objc_j2objc_annotations = True,
     omit_com_google_protobuf = True,
     omit_com_google_protobuf_javalite = True,
     omit_com_google_protobuf_nano_protobuf_javanano = True,