Misplaced quote in resulting luarocks.bat file

Line 699 is writing this in the .bat file.

~~~~
C:\luarocks\2.1>IF NOT "c:\luarocks52\share\lua\5.2\?.lua;c:\luarocks52\share\lua\5.2\?\init.lua;;" == "" ("SET LUA_PATH_5_2=c:\luarocks\2.1\lua\?.lua;c:\luarocks\2.1\lua\?\init.lua;c:\luarocks52\share\lua\5.2\?.lua;c:\luarocks52\share\lua\5.2\?\init.lua;;")
~~~~

Which prints an error: `The system cannot find the path specified.`

It only happens if env var LUA_PATH_5_2 has some value.
Merge pull request #220 from ignacio/patch-2

Misplaced quote in resulting luarocks.bat file