Add gem version and semver stability badges to README

[greysteil]

First of all, thanks for rspec-rails! I've used it on every Rails project I've ever worked on, and love it.

Would you be up for adding badges that display the current version on rspec-rails, and its semver stability? The former is pretty self-explanatory, the later is a new badge I've made that displays the percentage of rspec-rails users' CI runs that pass when updating rspec-rails between SemVer compatible versions. Data comes from Dependabot (disclosure: I built it).

I've also fixed the Code Climate badge in this PR (the URL must have changed on shields.io).

The badges now look like this:

[fables-tales]

@greysteil I'm disinclined to add the "semver stability" badge as I can't independently verify that it actually works, or is in any way meaningful in the ruby programming language. The others we will need to consider.

[greysteil]

👍 - I've removed that one. It works pretty well, and picks out the 3.6.1 -> 3.7.0 break, for example, but I appreciate it needs more thought than the other two.

[fables-tales]

LGTM

[greysteil]

Squashed into a single commit. Pretty innocuous change now, and you can confirm it renders here.

Separately, would love to talk you through the SemVer stability score if you're open to it?

[JonRowe]

If we want to have a coverage badge we need to setup coverage, it seems I'm not a member of the organisation, who initially configured RSpec on code climate?

[greysteil]

Just dug into the Code Climate issue. Looks like this commit switched us to shields.io endpoint that is no longer supported, but the original URL still works. I've updated the badge accordingly:

Turns out it was never meant to be coverage (my bad for switching the broken badge to that initially) - it's a "maintainability" badge.

[olleolleolle]

@greysteil Could you rebase your changes? They're neat.

[fables-tales]

@JonRowe I'm happy to merge this on green if you are.

[JonRowe]

I'm happy if the builds green

[greysteil]

Build is going to be ❌ without #2051.

[fables-tales]

@greysteil let's rebase this now that the rubygems fix is merged.

[benoittgt]

LGTM. Thanks! 🎉

[JonRowe]

❤️