fix one failing test, around mirror URL

plugins/python-build/test/mirror.bats

@@ -92,7 +92,7 @@ export PYTHON_BUILD_MIRROR_URL=http://mirror.example.com
 
   stub shasum true "echo $checksum"
   stub curl "-*I* : true" \
-    "-q -o * -*S* http://?*/$checksum : cp $FIXTURE_ROOT/package-1.0.0.tar.gz \$3" \
+    "-q -o * -*S* https://?*/$checksum : cp $FIXTURE_ROOT/package-1.0.0.tar.gz \$3" \
 
   install_fixture definitions/with-checksum
   [ "$status" -eq 0 ]