attempt to fix windows build

Signed-off-by: Nicolas De Loof <[email protected]>

requirements.txt

@@ -20,6 +20,7 @@ PySocks==1.6.7
 PyYAML==4.2b1
 requests==2.22.0
 six==1.12.0
+subprocess32==3.5.4; python_version < '3.2'
 texttable==1.6.2
 urllib3==1.24.2; python_version == '3.3'
 websocket-client==0.32.0