Update .travis.yml

.travis.yml

@@ -8,6 +8,18 @@ install: true
 env:
 - GO111MODULE=on
 
+branches:
+  only:
+    - master
+
+before_install:
+  - |
+      if ! git diff --name-only $TRAVIS_COMMIT_RANGE | grep -qvE '(.md)|(.html)|^(LICENSE)|^(docs)'
+      then
+        echo "Only docs were updated, not running the CI."
+        exit 0
+      fi
+
 before_script:
 - make install-linter