Add 2.3.5 back into the changelog

[karlbecker]

2.3.5 shows up in our package-lock when we had "ember-power-select": "^2.0.0", `, and I was looking for clues as to why we're seeing a weird error in our Ember 2.16 app during our production build process:

...
+- didFail
Error: Build Canceled: Broccoli Builder ran into an error with `broccoli-persistent-filter:Babel > [Babel: ember-basic-dropdown]` plugin. 💥
Worker is terminated
Error: Worker is terminated
...

...then I noticed 2.3.5 doesn't show up in the changelog!

I looked in the releases and found a change to changelog mentioning 2.3.5 in https://github.com/karlbecker/ember-power-select/commit/1e71541f52f0f24419e60c3cf621127ab1a5605a - was this version still supposed to be available to people?

I think the error we're dealing with is unrelated to 2.3.4 vs 2.3.5, but since I noticed 2.3.5 wasn't in the changelog, I think it's worth adding it back in.