Unconditionally support i128 on all versions

See slog-rs/slog#48e4651

Author: Techcable

build.rs

@@ -147,12 +147,10 @@ impl Serializer for ToSendSerializer {
         take(&mut self.kv, |kv| Box::new((kv, SingleKV(key, val))));
         Ok(())
     }
-    #[cfg(integer128)]
     fn emit_u128(&mut self, key: Key, val: u128) -> slog::Result {
         take(&mut self.kv, |kv| Box::new((kv, SingleKV(key, val))));
         Ok(())
     }
-    #[cfg(integer128)]
     fn emit_i128(&mut self, key: Key, val: i128) -> slog::Result {
         take(&mut self.kv, |kv| Box::new((kv, SingleKV(key, val))));
         Ok(())