io.c: fix typo

* io.c (rb_io_make_open_file): remove useless backslash.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47865 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

io.c

@@ -7420,7 +7420,7 @@ rb_io_make_open_file(VALUE obj)
     Check_Type(obj, T_FILE);
     if (RFILE(obj)->fptr) {
 	rb_io_close(obj);
-	rb_io_fptr_finalize(RFILE(obj)->fptr);\
+	rb_io_fptr_finalize(RFILE(obj)->fptr);
 	RFILE(obj)->fptr = 0;
     }
     fp = rb_io_fptr_new();