Fix Windows detection

The previous logic included "darwin" (i.e., macOS) and "cigwin", so it
wasn't really good at spotting what we wanted to.

Signed-off-by: Rodrigo Tobar <rtobar@icrar.org>

test/test_dump.py

@@ -14,7 +14,7 @@ def _do_test_dump(self, method, multiple_values):
         env['IJSON_BACKEND'] = 'python'
         # Ensure printing works on the subprocess in Windows
         # by using utf-8 on its stdout
-        if 'win' in sys.platform:
+        if sys.platform == 'win32':
             env = dict(os.environ)
             env['PYTHONIOENCODING'] = 'utf-8'
         cmd = [sys.executable, '-m', 'ijson.dump', '-m', method, '-p', '']