Fix import issue

src/objective-c/BUILD

@@ -180,6 +180,6 @@ load("@build_bazel_rules_apple//apple:resources.bzl", "apple_resource_bundle")
 apple_resource_bundle(
     # The choice of name is signicant here, since it determines the bundle name.
     name = "gRPCCertificates",
-    resources = ["etc/roots.pem"],
+    resources = ["//:etc/roots.pem"],
 )