fix file:close signature (#924)

quotes from Lua manual:

    When closing a file handle created with io.popen, file:close returns the same values returned by os.execute.

Author: fperrad

tl.lua

@@ -31,7 +31,7 @@ do
          "no" "full" "line"
       end
 
-      close: function(FILE): boolean, string, number
+      close: function(FILE): boolean, string, integer
       flush: function(FILE)
 
       lines: function(FILE): (function(): (string))

tl.tl

@@ -31,7 +31,7 @@ do
          "no" "full" "line"
       end
 
-      close: function(FILE): boolean, string, number
+      close: function(FILE): boolean, string, integer
       flush: function(FILE)
 
       lines: function(FILE): (function(): (string))