Use TLS 1.2 in Windows builds - #228

Step 7/8 : RUN Write-Host ('Installing pip=={0} ...' -f $env:PYTHON_PIP_VERSION); 	(New-Object System.Net.WebClient).DownloadFile('https://bootstrap.pypa.io/get-pip.py', 'get-pip.py'); 	python get-pip.py 		--disable-pip-version-check 		--no-cache-dir 		('pip=={0}' -f $env:PYTHON_PIP_VERSION) 	; 	Remove-Item get-pip.py -Force; 		Write-Host 'Verifying pip install ...'; 	pip --version; 		Write-Host 'Complete.';
 ---> Running in f1d24a39e5bd
Installing pip==9.0.1 ...
Exception calling "DownloadFile" with "2" argument(s): "The request was 
aborted: Could not create SSL/TLS secure channel."
At line:1 char:101
+ ... P_VERSION); (New-Object System.Net.WebClient).DownloadFile('https://b ...
+                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], ParentContainsErrorRecordE 
   xception
    + FullyQualifiedErrorId : WebException
 
The command 'powershell -Command $ErrorActionPreference = 'Stop'; Write-Host ('Installing pip=={0} ...' -f $env:PYTHON_PIP_VERSION); 	(New-Object System.Net.WebClient).DownloadFile('https://bootstrap.pypa.io/get-pip.py', 'get-pip.py'); 	python get-pip.py 		--disable-pip-version-check 		--no-cache-dir 		('pip=={0}' -f $env:PYTHON_PIP_VERSION) 	; 	Remove-Item get-pip.py -Force; 		Write-Host 'Verifying pip install ...'; 	pip --version; 		Write-Host 'Complete.';' returned a non-zero code: 1