Correct error message at pwd.lua

During investigation of the issues found that error message had
not user friendly format:
 local pwgr_errstr = "get%s failed [errno %d]: %s"
produced:
 [001] LuajitError: builtin/pwd.lua:101: getgetgrall failed [errno 2]: No such file or directory
while it had to be:
 [001] LuajitError: builtin/pwd.lua:101: getgrall failed [errno 2]: No such file or directory
Fixed the error message.

src/lua/pwd.lua

@@ -86,7 +86,7 @@ ffi.cdef[[
 
 -- {{{ Error handling
 
-local pwgr_errstr = "get%s failed [errno %d]: %s"
+local pwgr_errstr = "%s failed [errno %d]: %s"
 
 -- Use it in the following way: set errno to zero, call a passwd /
 -- group function, then call this function to check whether there