Simplify appveyor config

support/appveyor-build.py

@@ -5,7 +5,7 @@ import os
 from subprocess import check_call
 
 build = os.environ['BUILD']
-config = os.environ['CONFIG']
+config = os.environ['CONFIGURATION']
 path = os.environ['PATH']
 cmake_command = ['cmake', '-DFMT_PEDANTIC=ON', '-DCMAKE_BUILD_TYPE=' + config]
 if build == 'mingw':