Makes brotli-size an optional dep

[flovilmart]

Description

This PR removes Brotli-size as a dependency and puts it in the optional deps in order to provide node 10+ compatibility

Motivation and Context

The current implementation cannot be setup on any modern node system as Brotli-size fails to install due to native bindings not being available.

Changes

This is not a breaking change as users who require Brotli for size computation will see no change. Moving to a non supported version of node, Brotli-size will fail so install, which will in turn fail the test (which is better than failing to install this module altogether)

[flovilmart]

@siddharthkp is it something you are considering in order to bring compatibility to node 10+ or do you wish to not integrate this change?

[siddharthkp]

@flovilmart, can you mention the exact versions when you say:

The current implementation cannot be setup on any modern node system as Brotli-size fails to install due to native bindings not being available.

Context: I am able to install brotli-size on Node 8, 10 and 12 🤔

[flovilmart]

from what I recall, brotli-size depends on iltotb which provides native bindings for brotli. This project only publishes a handful of pre-built binaries. In certain environment, like a lightweight Docker builder image, the build tools necessary to build iltorb may not be installed. iltorb would then in turn not build, and this project would not install.

I believe the node version used was 10.15.3 on circle CI and heroku. It looks like the binaries are uploaded on iltorb releases now but that does not mean they were

I am not involved in the project that required this and perhaps @nicoespeon can track down the commit that made use of the fork in the project and provide additional context for this.