Bump uglifier from 4.1.17 to 4.1.20

Bumps [uglifier](https://github.com/lautis/uglifier) from 4.1.17 to 4.1.20.
- [Release notes](https://github.com/lautis/uglifier/releases)
- [Changelog](https://github.com/lautis/uglifier/blob/master/CHANGELOG.md)
- [Commits](https://github.com/lautis/uglifier/compare/v4.1.17...v4.1.20)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Gemfile.lock

@@ -58,8 +58,6 @@ GEM
     autoprefixer-rails (9.3.1)
       execjs
     bcrypt (3.1.12)
-    bootsnap (1.3.2)
-      msgpack (~> 1.0)
     bootstrap-sass (3.3.7)
       autoprefixer-rails (>= 5.2.1)
       sass (>= 3.3.4)
@@ -132,7 +130,6 @@ GEM
     minitest-stub-const (0.6)
     mocha (1.7.0)
       metaclass (~> 0.0.1)
-    msgpack (1.2.4)
     mysql2 (0.4.10)
     nio4r (2.3.1)
     nokogiri (1.8.5)
@@ -258,7 +255,7 @@ GEM
       sass
     tzinfo (1.2.5)
       thread_safe (~> 0.1)
-    uglifier (4.1.17)
+    uglifier (4.1.20)
       execjs (>= 0.3.0, < 3)
     unicode-display_width (1.4.0)
     uniform_notifier (1.12.1)
@@ -279,7 +276,6 @@ DEPENDENCIES
   activemodel-serializers-xml (~> 1.0.1)
   acts_as_list
   bcrypt (~> 3.1.7)
-  bootsnap (~> 1.1)
   bootstrap-sass (= 3.3.7)
   bullet
   byebug