Build PR branches only once (for origin branches) and skip docs changes

.github/workflows/test.yml

@@ -1,6 +1,11 @@
 name: Test
 
-on: [push, pull_request]
+on:
+  push:
+    - master
+  pull_request:
+    paths-ignore:
+      - 'docs/**'
 
 jobs:
   test:

.travis.yml

@@ -1,5 +1,9 @@
 language: minimal
 
+branches:
+  only:
+  - master
+
 jobs:
   include:
     - name: Linux | x86_64 + i686 | Python 3.5

appveyor.yml

@@ -19,3 +19,11 @@ install: python -m pip install -r requirements-dev.txt
 # the '-u' flag is required so the output is in the correct order.
 # See https://github.com/joerick/cibuildwheel/pull/24 for more info.
 test_script: python -u ./bin/run_tests.py
+
+branches:
+  only:
+    - master
+
+skip_commits:
+  files:
+    - docs/*