Update appveyor config. (#1299)

* pip is already installed by default. No need to install it manually, which was causing an error anyway.
* Confirm tox envs use correct Python version. The documentation at <https://packaging.python.org/guides/supporting-windows-using-appveyor/> seems to suggest it shouldn't work, but it clearly does.

appveyor.yml

@@ -19,10 +19,7 @@ environment:
     - TOXENV: flake8
 init:
   - "ECHO %TOXENV%"
-  - ps: "ls C:\\Python*"
 install:
-  - ps: Invoke-WebRequest "https://bootstrap.pypa.io/get-pip.py" -OutFile "c:\\get-pip.py"
-  - "c:\\python27\\python c:\\get-pip.py"
   - "c:\\python27\\Scripts\\pip install tox"
 test_script:
   - "git clean -f -d -x"

tox.ini

@@ -10,6 +10,7 @@ deps=
     py{27,33,34,35,36,py,py3}-min-req: -rrequirements/project-min.txt
     py{27,33,34,35,36,py,py3}-{unittests,min-req}: -rrequirements/test.txt
 commands=
+    {envpython} --version
     py{27,33,34,35,36,py,py3}-{unittests,min-req}: {envbindir}/nosetests --with-coverage --cover-package mkdocs mkdocs
     py{27,33,34,35,36,py,py3}-integration: {envpython} -m mkdocs.tests.integration --output={envtmpdir}/builds