[CI] Updates Regexp for license header script

Author: picandocodigo

.github/check_license_headers.rb

@@ -16,7 +16,7 @@
 # under the License.
 
 LICENSE = File.read('./.github/license-header.txt')
-files = `git ls-files | grep -E '\.rb|Rakefile|\.rake|\.erb|Gemfile|gemspec'`.split("\n")
+files = `git ls-files | grep -E '\.rb|Rakefile|\\.rake|\.erb|Gemfile|gemspec'`.split("\n")
 errors = []
 
 files.each do |file|