Build script fixes from v4 branch

Author: Zac-HD

scripts/basic-test.sh

@@ -24,7 +24,7 @@ PYTEST="python -m pytest -n2"
 
 $PYTEST --runpytest=subprocess tests/pytest
 
-pip install ".[datetime]"
+pip install ".[pytz]"
 $PYTEST tests/datetime/
 pip uninstall -y pytz
 

scripts/check-release-file.py

@@ -26,13 +26,17 @@
 
 sys.path.append(os.path.dirname(__file__))  # noqa
 
+DO_RELEASE_CHECK = os.environ.get('TRAVIS_BRANCH', 'master') == 'master'
 
 if __name__ == '__main__':
-    if tools.has_source_changes():
+    if DO_RELEASE_CHECK and tools.has_source_changes():
         if not tools.has_release():
             print(
                 'There are source changes but no RELEASE.rst. Please create '
                 'one to describe your changes.'
             )
             sys.exit(1)
         tools.parse_release_file()
+    else:
+        print('Skipping release check, because this is not the master branch '
+              'or the pull request is not targeting the master branch.')