Use DOCS_API_TOKEN for triggering docs build

Signed-off-by: Balasankar "Balu" C <balasankarc@autistici.org>

scripts/trigger-build

@@ -196,6 +196,10 @@ module Trigger
   end
 
   class Docs < Base
+    def self.access_token
+      ENV['DOCS_API_TOKEN']
+    end
+
     SUCCESS_MESSAGE = <<~MSG
     => You should now be able to preview your changes under the following URL: