skip overwriting files

Author: leafo

appveyor.yml

@@ -6,7 +6,7 @@ install:
   - ps: Start-FileDownload 'http://leafo.net/dump/lua5_1_4_Win32_dll8_lib.zip'
   - ps: Start-FileDownload 'http://leafo.net/dump/lua5_1_4_Win32_bin.zip'
   - 7z x lua5_1_4_Win32_dll8_lib.zip
-  - 7z x lua5_1_4_Win32_bin.zip
+  - 7z x lua5_1_4_Win32_bin.zip -aos
   - set PATH=C:\MinGW\bin;C:\MinGW\msys\1.0\bin;%PATH%
   - dir .