Bump autoprefixer-rails from 8.2.0 to 10.2.5.1

We're upgrading to this version in order because it's the first version
that works with our current version of execjs when running the
`autoprefixer:info` task. Since it's been such a long time since the
last time we upgraded autoprefixer-rails (version 8.2.0, which is the
version we were using, was released on March 2018), and we're getting a
warning when compiling the assets with the latest version, we're going
to do it gradually; version 10.2.5.1 was released on May 2021, so it
also seems like a reasonable middlepoint.

Note we're moving the `browserlist` file to `.browserlistrc` because
that's the expected locations in new versions of autoprefixer-rails.

Also note that we're changing this file so we support browsers released
in the last 7 years, so we still support more or less the same browsers
we supported before this change (about 98% of the browsers out there).
We might reduce it to 5 years in the future.

Bumps [autoprefixer-rails](https://github.com/ai/autoprefixer-rails) from 8.2.0 to 10.2.5.1
- [Changelog](https://github.com/ai/autoprefixer-rails/blob/master/CHANGELOG.md)
- [Commits](https://github.com/ai/autoprefixer-rails/compare/8.2.0...10.2.5.1

Gemfile

@@ -8,7 +8,7 @@ gem "ahoy_matey", "~> 5.0.2"
 gem "airbrake", "~> 13.0.4"
 gem "ancestry", "~> 4.3.3"
 gem "audited", "~> 5.4.3"
-gem "autoprefixer-rails", "~> 8.2.0"
+gem "autoprefixer-rails", "~> 10.2.5.1"
 gem "bing_translator", "~> 6.2.0"
 gem "cancancan", "~> 3.5.0"
 gem "caxlsx", "~> 4.1.0"

Gemfile.lock

@@ -87,8 +87,8 @@ GEM
     audited (5.4.3)
       activerecord (>= 5.0, < 7.2)
       request_store (~> 1.2)
-    autoprefixer-rails (8.2.0)
+    autoprefixer-rails (10.2.5.1)
-      execjs
+      execjs (> 0)
     base64 (0.1.1)
     bcrypt (3.1.20)
     better_html (2.0.2)
@@ -689,7 +689,7 @@ DEPENDENCIES
   airbrake (~> 13.0.4)
   ancestry (~> 4.3.3)
   audited (~> 5.4.3)
-  autoprefixer-rails (~> 8.2.0)
+  autoprefixer-rails (~> 10.2.5.1)
   bing_translator (~> 6.2.0)
   bullet (~> 7.1.6)
   byebug (~> 11.1.3)

app/assets/stylesheets/.browserslistrc

@@ -1,4 +1,5 @@
 last 2 versions
+last 7 years
 ie >= 9
 Android >= 2.3
 ios >= 7