Try to fix appveyor issues.

appveyor.yml

@@ -13,8 +13,9 @@ environment:
   global:
     # See: http://stackoverflow.com/a/13751649/163740
     WRAPPER: "cmd /E:ON /V:ON /C .\\scripts\\win_wrapper.cmd"
-    PIP:     "%WRAPPER% %PYTHON%\\Scripts\\pip.exe"
-    SETUPPY: "%WRAPPER% %PYTHON%\\python setup.py --with-extension"
+    PIP:     "%WRAPPER% %PYTHON%\\python.exe -m pip"
+    SETUPPY: "%WRAPPER% %PYTHON%\\python.exe setup.py --with-extension"
+    TWINE:   "%WRAPPER% %PYTHON%\\python.exe -m twine"
     PYPI_USERNAME: "earwigbot"
     PYPI_PASSWORD:
       secure: gOIcvPxSC2ujuhwOzwj3v8xjq3CCYd8keFWVnguLM+gcL0e02qshDHy7gwZZwj0+
@@ -28,14 +29,6 @@ environment:
       PYTHON_VERSION: "2.7"
       PYTHON_ARCH:    "64"
 
-    - PYTHON:         "C:\\Python33"
-      PYTHON_VERSION: "3.3"
-      PYTHON_ARCH:    "32"
-
-    - PYTHON:         "C:\\Python33-x64"
-      PYTHON_VERSION: "3.3"
-      PYTHON_ARCH:    "64"
-
     - PYTHON:         "C:\\Python34"
       PYTHON_VERSION: "3.4"
       PYTHON_ARCH:    "32"
@@ -60,6 +53,14 @@ environment:
       PYTHON_VERSION: "3.6"
       PYTHON_ARCH:    "64"
 
+    - PYTHON:         "C:\\Python37"
+      PYTHON_VERSION: "3.7"
+      PYTHON_ARCH:    "32"
+
+    - PYTHON:         "C:\\Python37-x64"
+      PYTHON_VERSION: "3.7"
+      PYTHON_ARCH:    "64"
+
 install:
   - "%PIP% install --disable-pip-version-check --user --upgrade pip"
   - "%PIP% install wheel twine"
@@ -74,7 +75,7 @@ after_test:
   - "%SETUPPY% bdist_wheel"
 
 on_success:
-  - "IF %APPVEYOR_REPO_BRANCH%==master %WRAPPER% %PYTHON%\\python -m twine upload dist\\* -u %PYPI_USERNAME% -p %PYPI_PASSWORD%"
+  - "IF %APPVEYOR_REPO_BRANCH%==master %TWINE% upload dist\\* -u %PYPI_USERNAME% -p %PYPI_PASSWORD%"
 
 artifacts:
   - path: dist\*