build: suppress ErrorProne DefaultPackage error in testdata (#4481)

diff --git a/kythe/javatests/com/google/devtools/kythe/analyzers/java/testdata/BUILD b/kythe/javatests/com/google/devtools/kythe/analyzers/java/testdata/BUILD
index fb9838e..e2fe08c 100644
--- a/kythe/javatests/com/google/devtools/kythe/analyzers/java/testdata/BUILD
+++ b/kythe/javatests/com/google/devtools/kythe/analyzers/java/testdata/BUILD
@@ -16,6 +16,7 @@
 java_library(
     name = "testdata",
     srcs = glob(["*.java"]),
+    javacopts = ["-Xep:DefaultPackage:OFF"],
     deps = ["@maven//:com_google_code_findbugs_jsr305"],  # needed for pkg/package-info.java
 )