Bazel: Automatically fix lint errors with buildifier

In recent buildifier versions, lint errors can be fixed automatically:

  $ find . \( -name BUILD -o -name "*.bzl" \) -print \
      | xargs buildifier --lint=fix

This commit was created with Buildifier version 0.19.2:

  $ buildifier --version
buildifier version: 0.19.2
buildifier scm revision: d39e4d5c25111527369142f16cdb49aa67707313

Change-Id: I1f06cd4596e794981ccc2d9fc2d1da9b17f3973a
diff --git a/tools/bzl/classpath.bzl b/tools/bzl/classpath.bzl
index afdd907..9ec5f15 100644
--- a/tools/bzl/classpath.bzl
+++ b/tools/bzl/classpath.bzl
@@ -7,8 +7,8 @@
         elif hasattr(d, "files"):
             all += d.files
 
-    as_strs = [c.path for c in all]
-    ctx.file_action(
+    as_strs = [c.path for c in all.to_list()]
+    ctx.actions.write(
         output = ctx.outputs.runtime,
         content = "\n".join(sorted(as_strs)),
     )