Bazel: Reformat build files

Reformat the Bazel build files with the buildifier tool [1].

The style is different for Bazel files. Most notably, indentation level
is 4 spaces instead of 2, and " is used instead of '.

[1] https://github.com/bazelbuild/buildifier

Change-Id: I95c0c6f11b6d76572797853b4ebb5cee5ebd3c98
diff --git a/tools/bzl/BUILD b/tools/bzl/BUILD
index bfbbd21..a0f5bd1 100644
--- a/tools/bzl/BUILD
+++ b/tools/bzl/BUILD
@@ -1,6 +1,5 @@
-
 exports_files([
-  "license-map.py",
-  "test_empty.sh",
-  "test_license.sh",
+    "license-map.py",
+    "test_empty.sh",
+    "test_license.sh",
 ])