ci(yamllint): add rule empty-values

* Automated using myii/ssf-formula#27

Author: myii

.travis.yml

@@ -26,20 +26,20 @@ env:
     # - INSTANCE: default-opensuse-leap-15-develop-py3
     # - INSTANCE: default-amazonlinux-2-develop-py2
     # - INSTANCE: default-debian-9-2019-2-py3
-    - INSTANCE: default-ubuntu-1804-2019-2-py3
+    # - INSTANCE: default-ubuntu-1804-2019-2-py3
     # - INSTANCE: default-centos-7-2019-2-py3
     # - INSTANCE: default-fedora-30-2019-2-py3
     # - INSTANCE: default-opensuse-leap-15-2019-2-py3
-    - INSTANCE: default-amazonlinux-2-2019-2-py2
+    # - INSTANCE: default-amazonlinux-2-2019-2-py2
     # - INSTANCE: default-debian-9-2018-3-py2
     # - INSTANCE: default-ubuntu-1604-2018-3-py2
-    - INSTANCE: default-centos-7-2018-3-py2
+    # - INSTANCE: default-centos-7-2018-3-py2
     # - INSTANCE: default-fedora-29-2018-3-py2
-    - INSTANCE: default-opensuse-leap-15-2018-3-py2
+    # - INSTANCE: default-opensuse-leap-15-2018-3-py2
     # - INSTANCE: default-amazonlinux-2-2018-3-py2
     # - INSTANCE: default-debian-8-2017-7-py2
     # - INSTANCE: default-ubuntu-1604-2017-7-py2
-    - INSTANCE: default-centos-6-2017-7-py2
+    # - INSTANCE: default-centos-6-2017-7-py2
     # - INSTANCE: default-fedora-29-2017-7-py2
     # - INSTANCE: default-opensuse-leap-15-2017-7-py2
     # - INSTANCE: default-amazonlinux-2-2017-7-py2

.yamllint

@@ -10,6 +10,9 @@ ignore: |
   node_modules/
 
 rules:
+  empty-values:
+    forbid-in-block-mappings: true
+    forbid-in-flow-mappings: true
   line-length:
     # Increase from default of `80`
     # Based on https://github.com/PyCQA/flake8-bugbear#opinionated-warnings (`B950`)