Fix coverage upload on Appveyor

Don't use 'shallow_clone' in appveyor.yml, it causes
.git/ missing. Also remove an old caching option.

appveyor.yml

@@ -1,10 +1,5 @@
 version: 1.0.{build}
 
-shallow_clone: true
-
-cache:
-  - downloads
-
 environment:
   matrix:
   - Python: 35-x64
@@ -19,5 +14,4 @@ test_script:
   - pep8 .
   - nosetests
   - coverage report
-  - git rev-parse --abbrev-ref HEAD
   - if not "%COVERALLS_REPO_TOKEN%"=="" coveralls