feat(buck): add support for buck2 files (#188)

ISSUE: #188

Buck2 is a hermetic build system similar to Bazel
but written in Rust.

CHANGELOG:
- [ ] Update comment group for '#' style comments.
- [ ] Update test to ensure detection works.

Author: yesudeep

main.go

@@ -320,6 +320,7 @@ func licenseHeader(path string, tmpl *template.Template, data licenseData) ([]by
 		lic, err = executeTemplate(tmpl, data, "", "// ", "")
 	case
 		".awk",
+		".buckconfig", "buck",
 		".bzl", ".bazel", "build", ".build",
 		".dockerfile", "dockerfile",
 		".ex", ".exs",

main_test.go

@@ -345,6 +345,7 @@ func TestLicenseHeader(t *testing.T) {
 		{
 			[]string{
 				"f.awk",
+				"f.buckconfig", "buck",
 				"f.bzl", "f.bazel", "build", "f.build",
 				"f.dockerfile", "dockerfile",
 				"f.ex", "f.exs",