(maint) Add master back to travis for testing

Prior to this commit, the master branch was removed from the travis CI
testing. This commit adds it back into the configuration.

Author: Jarret Lavallee

.sync.yml

@@ -13,3 +13,9 @@ spec/default_facts.yml:
     pe_server_version: '2016.4.5'
 .rubocop.yml:
   selected_profile: off
+
+.travis.yml:
+  branches:
+    - master
+    - main
+    - /^v\d/

.travis.yml

@@ -45,5 +45,6 @@ branches:
   only:
     - main
     - /^v\d/
+    - master
 notifications:
   email: false