[ruby/etc] bump up to 1.3.1

https://github.com/ruby/etc/commit/82dd69a4cf

ext/etc/etc.c

@@ -52,7 +52,7 @@ char *getenv();
 #endif
 char *getlogin();
 
-#define RUBY_ETC_VERSION "1.3.0"
+#define RUBY_ETC_VERSION "1.3.1"
 
 #ifdef HAVE_RB_DEPRECATE_CONSTANT
 void rb_deprecate_constant(VALUE mod, const char *name);