Bump middleman-autoprefixer from 2.10.1 to 3.0.0 (#399)

Bumps [middleman-autoprefixer](https://github.com/middleman/middleman-autoprefixer) from 2.10.1 to 3.0.0.
- [Release notes](https://github.com/middleman/middleman-autoprefixer/releases)
- [Changelog](https://github.com/middleman/middleman-autoprefixer/blob/master/CHANGELOG.md)
- [Commits](middleman/middleman-autoprefixer@v2.10.1...v3.0.0)

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Gemfile.lock

@@ -1,15 +1,15 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    activesupport (5.2.5)
+    activesupport (5.2.6)
       concurrent-ruby (~> 1.0, >= 1.0.2)
       i18n (>= 0.7, < 2)
       minitest (~> 5.1)
       tzinfo (~> 1.1)
     addressable (2.8.0)
       public_suffix (>= 2.0.2, < 5.0)
-    autoprefixer-rails (9.4.10.2)
-      execjs
+    autoprefixer-rails (10.2.5.0)
+      execjs (< 2.8.0)
     backports (3.21.0)
     coderay (1.1.3)
     coffee-script (2.4.1)
@@ -51,9 +51,9 @@ GEM
       kramdown (>= 2.3.0)
       middleman-cli (= 4.3.11)
       middleman-core (= 4.3.11)
-    middleman-autoprefixer (2.10.1)
-      autoprefixer-rails (~> 9.1)
-      middleman-core (>= 3.3.3)
+    middleman-autoprefixer (3.0.0)
+      autoprefixer-rails (~> 10.0)
+      middleman-core (>= 4.0.0)
     middleman-blog (4.0.3)
       addressable (~> 2.3)
       middleman-core (>= 4.0.0)
@@ -111,7 +111,7 @@ GEM
     rack-livereload (0.3.17)
       rack
     rake (13.0.1)
-    rb-fsevent (0.10.4)
+    rb-fsevent (0.11.0)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
     redcarpet (3.5.1)