remove same-named wheel before shutil.move

In adobe-type-tools/afdko#595 we attempt to build a py2.py3 wheel
thus the filename of the wheel is the same as the previous ones, and it causes a shutil.Error
https://travis-ci.org/adobe-type-tools/afdko/jobs/424691105#L1460

just remove the previous existing file before moving the new one (they'll be identical anyway,
or at least they *should*).

cibuildwheel/macos.py

@@ -130,5 +130,8 @@ def call(args, env=None, cwd=None, shell=False):
             test_command_prepared = prepare_command(test_command, project=abs_project_dir)
             call(test_command_prepared, cwd=os.environ['HOME'], env=env, shell=True)
 
-        # we're all done here; move it to output
-        shutil.move(delocated_wheel, output_dir)
+        # we're all done here; move it to output (remove if already exists)
+        dst = os.path.join(output_dir, os.path.basename(delocated_wheel))
+        if os.path.isfile(dst):
+            os.remove(dst)
+        shutil.move(delocated_wheel, dst)

cibuildwheel/windows.py

@@ -101,5 +101,8 @@ def shell(args, env=None, cwd=None):
             test_command_prepared = prepare_command(test_command, project=abs_project_dir)
             shell([test_command_prepared], cwd='c:\\', env=env)
 
-        # we're all done here; move it to output
-        shutil.move(built_wheel, output_dir)
+        # we're all done here; move it to output (remove if already exists)
+        dst = os.path.join(output_dir, os.path.basename(built_wheel))
+        if os.path.isfile(dst):
+            os.remove(dst)
+        shutil.move(built_wheel, dst)