Format bzl files with buildifier version 1.0.0

Update the contribution documentation to recommend using buildifier
version 1.0.0.

Use version 1.0.0 to reformat bzl files with --lint=fix.

Note: Usually we include the output of `buildifier --version' in the
commit message, but in this version it is broken and doesn't provide
any meaningful information. See [1].

[1] https://github.com/bazelbuild/buildtools/issues/782

Change-Id: Id3392bae5115e3cd52ad910fa7b1a38e06cf28cb

tools/bzl/js.bzl

diff --git a/tools/bzl/js.bzl b/tools/bzl/js.bzl
index 8184d75..d637ad4 100644
--- a/tools/bzl/js.bzl
+++ b/tools/bzl/js.bzl
@@ -526,7 +526,7 @@
                 cmd = "cp $(SRCS) $(@D)",
                 output_to_bindir = True,
             )
-            static_files += [":" + name + "_copy_assets"]
+            static_files.append(":" + name + "_copy_assets")
 
     native.filegroup(
         name = name,