Fix requirements installing on Appveyor

.appveyor.yml

@@ -5,6 +5,7 @@ cache:
 build: off
 environment:
     PYTHONUNBUFFERED: 1
+    VIRTUALENV_DOWNLOAD: no
     matrix:
     - TESTENV: py34
     - TESTENV: unittests-frozen

scripts/dev/ci/appveyor_install.py

@@ -66,8 +66,8 @@ print("Installing PyQt5...")
 subprocess.check_call([r'C:\install-PyQt5.exe', '/S'])
 
 print("Installing pip/tox")
-pip_install(r'scripts\dev\ci\requirements-pip.txt')
-pip_install(r'scripts\dev\ci\requirements-tox.txt')
+pip_install(r'-rscripts\dev\ci\requirements-pip.txt')
+pip_install(r'-rscripts\dev\ci\requirements-tox.txt')
 
 print("Linking Python...")
 with open(r'C:\Windows\system32\python3.bat', 'w') as f: