Do not update pip on Azure

Avoid upgrading pip because it is giving this error on py34:

Requirement already up-to-date: pip in c:\hostedtoolcache\windows\python\3.4.4\x64\lib\site-packages (19.2.1)
ERROR: Package 'pip' requires a different Python: 3.4.4 not in '>=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*'
[error]Cmd.exe exited with code '1'.

Author: nicoddemus

azure-pipelines.yml

@@ -91,7 +91,7 @@ jobs:
     condition: eq(variables['python.needs_vc'], True)
     displayName: 'Install VC for py27'
 
-  - script: python -m pip install --upgrade pip && python -m pip install tox
+  - script: python -m pip install tox
     displayName: 'Install tox'
 
   - script: |