Cleanup post luafilesystem version de-underscoring (#2683)

The upstream luafilesystem tarball/version had a wayward/inconsistent
underscore in their more recent version tag.  The played badly with
our package fetching machinery (due to recent changes?).

Upstream cleaned up their bit which required some touchups here.

- updated the url
- updated the version (digest)
- updated the format statement for the path to the rockspec.

var/spack/repos/builtin/packages/lua-luafilesystem/package.py

@@ -36,16 +36,16 @@ class LuaLuafilesystem(Package):
     """
 
     homepage = 'http://keplerproject.github.io/luafilesystem'
-    url = 'https://github.com/keplerproject/luafilesystem/archive/v_1_6_3.tar.gz'
+    url = 'https://github.com/keplerproject/luafilesystem/archive/v1_6_3.tar.gz'
 
-    version('1_6_3', 'd0552c7e5a082f5bb2865af63fb9dc95')
+    version('1_6_3', 'bed11874cfded8b4beed7dd054127b24')
 
     depends_on('git@2.9.3:', type='build')
     extends('lua')
 
     def install(self, spec, prefix):
         rockspec_fmt = join_path(self.stage.path,
-                                 'luafilesystem-v_{version.underscored}',
+                                 'luafilesystem-{version.underscored}',
                                  'rockspecs',
                                  'luafilesystem-{version.dotted}-1.rockspec')
         luarocks('--tree=' + prefix, 'install',