Add Python 3.7 to AppVeyor Windows build/test

Author: tleonhardt

.appveyor.yml

@@ -4,4 +4,4 @@ install:
 build: off
 
 test_script:
-  - python -m tox -e py35-win,py36-win
+  - python -m tox -e py35-win,py36-win,py37-win

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py34,py35,py36,py37,py35-win,py36-win
+envlist = py34,py35,py36,py37,py35-win,py36-win,py37-win
 
 [pytest]
 testpaths = tests
@@ -73,3 +73,13 @@ deps =
   wcwidth
 commands = py.test -v
 
+[testenv:py37-win]
+deps =
+  codecov
+  pyperclip
+  pyreadline
+  pytest
+  pytest-cov
+commands =
+  py.test {posargs} --cov
+  codecov