Use pytest instead of py.test

Author: chinyeungli

appveyor.yml

@@ -7,7 +7,7 @@ build: off
 
 test_script:
     - set
-    - py.test -vvs tests
+    - pytest -vvs tests
 
 on_success:
   - "python etc/scripts/irc-notify.py aboutcode [{project_name}:{branch}] {short_commit}: \"{message}\" ({author}) {color_green}Succeeded,Details: {build_url},Commit: {commit_url}"