No longer use wercker for CI service

wercker.yml

@@ -1,19 +0,0 @@
-box:
-  id: ubuntu:trusty
-build:
-  steps:
-    - install-packages:
-        packages: python python3 pypy python-pip
-    - script:
-        name: python versions
-        code: |
-           python --version
-           python3 --version
-    - pip-install:
-        requirements_file: "test-requirements.txt"
-        packages_list: "tox"
-    - script:
-        name: tests
-        code: |
-           tox
-           COVERALLS_REPO_TOKEN=r9pnKBevvgJu7kUvP61BwFxodyKUq8vIO coveralls