AppVeyor: quench pip deprecation warnings for v2.7

Author: wjakob

.appveyor.yml

@@ -42,8 +42,8 @@ install:
     if ($env:PYTHON) {
       if ($env:PLATFORM -eq "x64") { $env:PYTHON = "$env:PYTHON-x64" }
       $env:PATH = "C:\Python$env:PYTHON\;C:\Python$env:PYTHON\Scripts\;$env:PATH"
-      python -m pip install --upgrade pip wheel
-      python -m pip install pytest numpy --no-warn-script-location
+      python -W ignore -m pip install --upgrade pip wheel
+      python -W ignore -m pip install pytest numpy --no-warn-script-location
     } elseif ($env:CONDA) {
       if ($env:CONDA -eq "27") { $env:CONDA = "" }
       if ($env:PLATFORM -eq "x64") { $env:CONDA = "$env:CONDA-x64" }