Fix git command...

extra/appveyor/appveyor.yml

@@ -28,7 +28,7 @@ install:
 - for /D %%i in (*) do @if "%%i" NEQ "love" @move %%i love\%%i
 - for %%i in (*) do @if "%%i" NEQ "appveyor.yml" @move %%i love\%%i
 # clone megasource and move into top directory.
-- git clone --depth 1 --single-branch -branch 12.x https://github.com/love2d/megasource.git megasource
+- git clone --depth 1 --single-branch --branch 12.x https://github.com/love2d/megasource.git megasource
 - cd megasource
 - for /D %%i in (*) do @move %%i ..\%%i
 - for %%i in (*) do @move %%i ..\%%i