7286: Fix documents to refer to URLs with https r=deivid-rodriguez a=giraffate

### What was the end-user problem that led to this PR?

End-users experience 301 redirect,  or unintentionally visit URL with http and may send email.

### What was your diagnosis of the problem?

I noticed the problem when I was reading codes. Following are some examples using curl to explain this problem.

```
curl -I http://slack.bundler.io/
HTTP/1.1 200 OK
Server: Cowboy
Connection: keep-alive
X-Powered-By: Express
Content-Type: text/html; charset=utf-8
Content-Length: 3726
Etag: W/"3Shz0DQR5y/DyBrYbyUBAQ=="
Date: Fri, 09 Aug 2019 14:16:23 GMT
Via: 1.1 vegur
```
```
curl -I http://contributor-covenant.org
HTTP/1.1 301 Moved Permanently
Cache-Control: public, max-age=0, must-revalidate
Content-Length: 49
Content-Type: text/plain
Date: Sun, 04 Aug 2019 09:47:02 GMT
Location: https://contributor-covenant.org/
Age: 448201
Connection: keep-alive
Server: Netlify
X-NF-Request-ID: 3de60b71-391e-4a6e-8cd4-74a12f217c80-14980829
```

### What is your fix for the problem, implemented in this PR?

My fix is to replace http URLs with https URLs.

### Why did you choose this fix out of the possible options?

It's because this fix is simple and easy.


Co-authored-by: Takayuki Nakata <f.seasons017@gmail.com>

7285: Bump rspec dependency to 3.8 r=deivid-rodriguez a=deivid-rodriguez

### What was the end-user problem that led to this PR?

The problem was that tests fail using rspec 3.7 or older.

### What was your diagnosis of the problem?

My diagnosis was that we're using `config.bisect_runner` which is only available from 3.8.

### What is your fix for the problem, implemented in this PR?

My fix is to bump the requirement.

Co-authored-by: David Rodríguez <deivid.rodriguez@riseup.net>

Because we're using `config.bisect_runner` which is only available from
3.8.