strict = true does not work in 0.22

[tkf]

It seems Documenter 0.22 does not fail on doctest failure even with strict = true?

$ julia --startup-file=no -q
shell> cat docs/src/index.md
# MyPlayground.jl

```jldoctest
julia> 1
2
```

shell> cat docs/make.jl
using Documenter
using MyPlayground

makedocs(
    sitename = "MyPlayground",
    modules = [MyPlayground],
    strict = true,
)

julia> include("docs/make.jl")
[ Info: SetupBuildDirectory: setting up build directory.
[ Info: ExpandTemplates: expanding markdown templates.
[ Info: CrossReferences: building cross-references.
[ Info: CheckDocument: running document checks.
┌ Error: doctest failure in src/index.md:3-6
│
│ ```jldoctest
│ julia> 1
│ 2
│ ```
│
│ Subexpression:
│
│ 1
│
│ Output:
│
│ 2
│
│ Expected output:
│
│ 1
│
│   diff = 21
└ @ Documenter.DocTests ~/.julia/packages/Documenter/G5Sup/src/DocTests.jl:264
[ Info: Populate: populating indices.
[ Info: RenderDocument: rendering document.
[ Info: HTMLWriter: rendering HTML pages.

(v1.3) pkg> st Documenter
    Status `~/.julia/environments/v1.3/Project.toml`
  [e30172f5] Documenter v0.22.3
  [682c06a0] JSON v0.20.0

See the example run on Travis:

• Correctly fails with 0.21: https://travis-ci.org/tkf/MyPlayground.jl/builds/525400153
• Incorrectly reports success with 0.22: https://travis-ci.org/tkf/MyPlayground.jl/builds/525400379