all: rename Bazel workspace to io_grpc_grpc_java

Fixes #4095
diff --git a/WORKSPACE b/WORKSPACE
index e0ae4f0..65bf26a 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -1,4 +1,4 @@
-workspace(name = "grpc_java")
+workspace(name = "io_grpc_grpc_java")
 
 load("//:repositories.bzl", "grpc_java_repositories")