Update the version number of figwheel-sidecar in the ProtoREPL instructions

[mpcarolin]

I followed the instructions at https://clojurescript.org/tools/atom#proto-repl and I encountered an issue running this command, as listed in the instructions:

(do (use 'figwheel-sidecar.repl-api) (start-figwheel!) (cljs-repl))

This threw a spec error, the same one shown here and here, and I couldn't run the REPL. Most likely one of my dependencies uses an older version of clojure.async that causes this problem.

I followed @bhauman's instructions from this comment, by bumping up the figwheel-sidecar dependency to 0.5.10. After that, I was able to run the clojurescript repl in the atom protorepl.

I propose at minimum updating the figwheel-sidecar version to 5.10 to prevent new users to the protoREPL from encountering this. The whole dependencies section could possibly use some updating, though.

I also tested this on a brand new app built using the template from "lein new figwheel ...". Everything worked as expected.

*Edit: this all occurred while running Clojure 1.9.0 and Clojurescript 1.10.238

[swannodette]

PR welcome!