Add headers to Makefiles also

Ensure makefiles also get license headers.

main.go

@@ -293,7 +293,7 @@ func licenseHeader(path string, tmpl *template.Template, data licenseData) ([]by
  lic, err = executeTemplate(tmpl, data, "/**", " * ", " */")
  case ".cc", ".cpp", ".cs", ".go", ".hcl", ".hh", ".hpp", ".m", ".mm", ".proto", ".rs", ".swift", ".dart", ".groovy", ".v", ".sv":
  lic, err = executeTemplate(tmpl, data, "", "// ", "")
- case ".py", ".sh", ".yaml", ".yml", ".dockerfile", "dockerfile", ".rb", "gemfile", ".tcl", ".bzl", ".pl", ".pp":
+ case ".py", ".sh", ".yaml", ".yml", ".dockerfile", "dockerfile", ".rb", "gemfile", ".tcl", ".bzl", ".pl", ".pp", "makefile":
  lic, err = executeTemplate(tmpl, data, "", "# ", "")
  case ".el", ".lisp":
  lic, err = executeTemplate(tmpl, data, "", ";; ", "")

main_test.go

@@ -316,7 +316,7 @@ func TestLicenseHeader(t *testing.T) {
  "// HYS\n\n",
  },
  {
- []string{"f.py", "f.sh", "f.yaml", "f.yml", "f.dockerfile", "dockerfile", "f.rb", "gemfile", "f.tcl", "f.bzl", "f.pl", "f.pp"},
+ []string{"f.py", "f.sh", "f.yaml", "f.yml", "f.dockerfile", "dockerfile", "f.rb", "gemfile", "makefile", "f.tcl", "f.bzl", "f.pl", "f.pp"},
  "# HYS\n\n",
  },
  {

testdata/expected/Makefile

@@ -0,0 +1,17 @@
+# Copyright 2018 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http:https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+.PHONY: example
+example:
+ echo "This is an example makefile and should have a header"

testdata/initial/Makefile

@@ -0,0 +1,3 @@
+.PHONY: example
+example:
+ echo "This is an example makefile and should have a header"