Add stacks table to workaround release issues (#210)

buildpack.toml

@@ -11,6 +11,13 @@ keywords = ["procfile", "processes", "heroku"]
 [[buildpack.licenses]]
 type = "BSD-3-Clause"
 
+# [[stacks]] is deprecated in Buildpack API 0.10, but is (unintentionally?)
+# required by `pack buildpack package`. The [[stacks]] table should be
+# removed when the issue (https://github.com/buildpacks/pack/issues/2047) is
+# resolved.
+[[stacks]]
+id = "*"
+
 [[targets]]
 os = "linux"
 arch = "amd64"