Fix Percy CI tests

[etpinard]

The Percy tests are currently failing, for example in #176:

• https://app.circleci.com/pipelines/github/plotly/Dash.jl/331/workflows/c2e84f85-414a-4a72-9eef-71354bc34ba7/jobs/435
• https://percy.io/plotly/dash.jl/builds/23374298/failed

If anyone seeing this has experience with Percy, your help would be much appreciated!

[etpinard]

Update

Now that #207 is merged, the CircleCI workflow now passes and can successfully upload percy snapshots to percy.io:

• https://app.circleci.com/pipelines/github/plotly/Dash.jl/386/workflows/8bbbdba0-347e-4ec1-88b7-94ef79a3df02/jobs/459
• https://percy.io/plotly/dash.jl/builds/28145762/changed/1564719617?browser=firefox&browser_ids=38%2C39&subcategories=unreviewed%2Cchanges_requested&viewLayout=side-by-side&viewMode=new&width=1280&widths=1280

But on the percy.io build page, looks like I can't approve the snapshots and we cannot reuse the "old" snapshots either.

So, looks like we'll need help from someone at Plotly in order to resolve this issue.

---

In the meantime, manually asserting that the screenshots look like:

is better than nothing 😄

[alexcjohnson]

@etpinard I sent you an invite to percy, LMK if that unblocks you!

[etpinard]

Thanks @alexcjohnson !!

I can now approve the baselines and I think I got the baseline settings to work correctly with

I got a clean pass in https://percy.io/plotly/dash.jl/builds/28183626/unchanged/1566645204?browser=chrome&viewLayout=side-by-side&viewMode=new&width=1280

and I got percy to generate a diff with this patch

--- a/test/integration/base/jl_render/jltr001r_undo_redo.jl
+++ b/test/integration/base/jl_render/jltr001r_undo_redo.jl
@@ -4,7 +4,8 @@ app = dash(show_undo_redo=true)

 app.layout = html_div() do
  dcc_input(id="a"),
- html_div(id="b")
+ html_div(id="b"),
+ html_h1("SHOULD NOT WORK")
 end

https://percy.io/plotly/dash.jl/builds/28184515/changed/1566701020?browser=firefox&browser_ids=38%2C39&subcategories=unreviewed%2Cchanges_requested&viewLayout=side-by-side&viewMode=new&width=1280&widths=1280

---

Closing 🎉 🎉 🎉