Add PR support to travis config

Thank you @setenforce0

.travis.yml

@@ -1,6 +1,7 @@
 jobs:
   include:
     - stage: build
+      if: (NOT type IN (pull_request)) AND (branch = master)
       language: minimal
       services:
         - docker
@@ -19,6 +20,7 @@ jobs:
         - echo $DOCKERHUB_PASSWORD | docker login -u $DOCKERHUB_USERNAME --password-stdin
         - docker push $IMAGE_NAME:latest
     - stage: test
+      if: (NOT type IN (pull_request)) AND (branch = master)
       sudo: required
       dist: bionic
       language: python
@@ -38,3 +40,25 @@ jobs:
         - sleep 10
         - cd tests
         - pytest --headless -n 8 --reruns 10 --reruns-delay 2
+    - stage: pr
+      if: type IN (pull_request)
+      sudo: required
+      dist: bionic
+      language: python
+      addons:
+        chrome: stable
+      python:
+        - 3.6
+      services:
+        - docker
+        - xvfb
+      script:
+        - sudo apt update
+        - sudo apt install --force-yes chromium-browser chromium-chromedriver
+        - pip3 install --upgrade pip
+        - pip3 install -U seleniumbase pytest
+        - docker build -t $IMAGE_NAME:$TRAVIS_COMMIT .
+        - docker run -d -p 127.0.0.1:8080:8080/tcp $IMAGE_NAME:$TRAVIS_COMMIT
+        - sleep 10
+        - cd tests
+        - pytest --headless -n 8 --reruns 10 --reruns-delay 2