pin pendulum to a version that will install on Windows.

Should be unpinned if python-pendulum/pendulum#365
is ever fixed, but right now pycounter won't install cleanly on
Windows (including on Appveyor) or anywhere the locale isn't set to
use UTF-8.

setup.py

@@ -13,7 +13,13 @@
 with open("README.rst") as readmefile:
     readme = readmefile.read()
 
-requirements = ["openpyxl", "requests", "six", "pendulum", "click"]
+requirements = [
+    "openpyxl",
+    "requests",
+    "six",
+    "pendulum==2.0.2",  # FIXME: Unpin once poetry fixes its utf-8 issues
+    "click",
+]
 
 if platform.python_implementation() == "PyPy":
     requirements.append("lxml<=3.4.4")