Make proposals map test more robust

We were testing what happens when clicking on a geozone without HTML
coordinates, which won't happen in a real browser.

So we're now defining the HTML coordinates and clicking on the area in
the test, which is what real people will do.

We also avoid having two consecutive `visit` calls, which will interfere
with the way we plan to test the presence of the <main> tag after every
`visit`.

Note that, the test didn't work with the HTML coordinates defined in the
`with_html_coordinates` trait, with Capybara showing the following
error:

```
Selenium::WebDriver::Error::ElementClickInterceptedError:
element click intercepted: Element
  <area shape="poly"
  coords="30,139,45,153,77,148,107,165"
  href="/proposals?search=California"
  title="California" alt="California">
is not clickable at point (413, 456).
Other element would receive the click:
  <img usemap="#map" src="/assets/map.jpg">
```

The cause of this error was the strange shape of the polygon, which was
greatly concave and and so the middle of its area wasn't part of it.
We're changing the polygon so it's now convex and when Capybara clicks
on its middle point everything will work as expected.

spec/factories/administration.rb

@@ -15,7 +15,7 @@ FactoryBot.define do
     end
 
     trait :with_html_coordinates do
-      html_map_coordinates { "30,139,45,153,77,148,107,165" }
+      html_map_coordinates { "30,139,45,153,77,148,107,125" }
     end
 
     trait :with_geojson do

spec/system/proposals_spec.rb

@@ -1353,8 +1353,8 @@ describe "Proposals" do
 
   context "Filter" do
     context "By geozone" do
-      let(:california) { Geozone.create(name: "California") }
+      let(:california) { create(:geozone, :with_html_coordinates, name: "California") }
-      let(:new_york)   { Geozone.create(name: "New York") }
+      let(:new_york)   { create(:geozone, name: "New York") }
 
       before do
         create(:proposal, geozone: california, title: "Bigger sequoias")
@@ -1362,14 +1362,11 @@ describe "Proposals" do
         create(:proposal, geozone: new_york, title: "Sully monument")
       end
 
-      scenario "From map", :no_js do
+      scenario "From map" do
         visit proposals_path
 
         click_link "map"
-        within("#html_map") do
+        within("#html_map") { find("area[title='California']").click }
-          url = find("area[title='California']")[:href]
-          visit url
-        end
 
         within("#proposals") do
           expect(page).to have_css(".proposal", count: 2)