Update .appveyor.yml.

.appveyor.yml

@@ -15,9 +15,9 @@ environment:
 
 install:
   - "%PYTHON%\\python.exe -m pip install -U pip"
-  - "%PYTHON%\\python.exe -m pip install -U pytest"
-  - "%PYTHON%\\python.exe -m pip install -r requirements.txt"
   - "%PYTHON%\\python.exe -m pip install wheel"
+  - "%PYTHON%\\python.exe -m pip install -r requirements.txt"
+  - "%PYTHON%\\python.exe -m pip install -U pytest"
 
 build: off