Don’t downgrade pip on windows wheel building (#5015)

* Don’t downgrade pip on windows wheel building

* Conditionally install enum34

* Syntax

.azure-pipelines/wheel-builder.yml

@@ -106,7 +106,7 @@ jobs:
  displayName: Create virtualenv
  - script: .venv/bin/pip install -U pip==10.0.1
  displayName: Downgrade pip lol
- - script: .venv/bin/pip install cffi six ipaddress enum34
+ - script: .venv/bin/pip install cffi six ipaddress "enum34; python_version < '3'"
  displayName: Install our Python dependencies
  - script: |
  set -e
@@ -215,9 +215,8 @@ jobs:
  OPENSSL_DIR: 'OpenSSL-Win64-2015'
  WINDOWS_ARCH: 'x86_64'
  steps:
- - script: '"C:/Python%PYTHON_VERSION%/python.exe" -m pip install -U pip==10.0.1'
- displayName: Downgrade pip lol
- - script: '"C:/Python%PYTHON_VERSION%/Scripts/pip" install wheel cffi six ipaddress enum34'
+ - script: |
+ "C:/Python%PYTHON_VERSION%/Scripts/pip" install cffi six ipaddress "enum34; python_version < '3'"
  displayName: Install wheel and our Python dependencies
  - script: |
  set INCLUDE=C:/%OPENSSL_DIR%/include;%INCLUDE%