Bump poltergeist from 1.17.0 to 1.18.1

Bumps [poltergeist](https://github.com/teampoltergeist/poltergeist) from 1.17.0 to 1.18.1.
- [Release notes](https://github.com/teampoltergeist/poltergeist/releases)
- [Changelog](https://github.com/teampoltergeist/poltergeist/blob/master/CHANGELOG.md)
- [Commits](teampoltergeist/poltergeist@v1.17.0...v1.18.1)

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

Gemfile.lock

@@ -48,8 +48,8 @@ GEM
       i18n (>= 0.7, < 2)
       minitest (~> 5.1)
       tzinfo (~> 1.1)
-    addressable (2.5.2)
-      public_suffix (>= 2.0.2, < 4.0)
+    addressable (2.7.0)
+      public_suffix (>= 2.0.2, < 5.0)
     arel (9.0.0)
     autoprefixer-rails (9.4.8)
       execjs
@@ -162,15 +162,16 @@ GEM
       mime-types-data (~> 3.2015)
     mime-types-data (3.2016.0521)
     mimemagic (0.3.6)
-    mini_mime (1.0.1)
-    mini_portile2 (2.4.0)
+    mini_mime (1.0.2)
+    mini_portile2 (2.5.0)
     minitest (5.14.1)
     multi_json (1.13.1)
     multi_xml (0.6.0)
     multipart-post (2.0.0)
     nio4r (2.3.1)
-    nokogiri (1.10.9)
-      mini_portile2 (~> 2.4.0)
+    nokogiri (1.11.2)
+      mini_portile2 (~> 2.5.0)
+      racc (~> 1.4)
     oauth2 (1.4.0)
       faraday (>= 0.8, < 0.13)
       jwt (~> 1.0)
@@ -186,8 +187,8 @@ GEM
       terrapin (~> 0.6.0)
     pg (1.1.2)
     phantomjs (2.1.1.0)
-    poltergeist (1.17.0)
-      capybara (~> 2.1)
+    poltergeist (1.18.1)
+      capybara (>= 2.1, < 4)
       cliver (~> 0.3.1)
       websocket-driver (>= 0.2.0)
     postmark (1.21.1)
@@ -200,8 +201,9 @@ GEM
       method_source (~> 0.9.0)
     pry-rails (0.3.6)
       pry (>= 0.10.4)
-    public_suffix (3.0.2)
+    public_suffix (4.0.6)
     puma (3.12.6)
+    racc (1.5.2)
     rack (2.2.3)
     rack-cors (1.0.5)
       rack (>= 1.6.0)
@@ -307,10 +309,10 @@ GEM
       activemodel (>= 5.0)
       bindex (>= 0.4.0)
       railties (>= 5.0)
-    websocket-driver (0.7.0)
+    websocket-driver (0.7.3)
       websocket-extensions (>= 0.1.0)
-    websocket-extensions (0.1.3)
-    xpath (3.0.0)
+    websocket-extensions (0.1.5)
+    xpath (3.2.0)
       nokogiri (~> 1.8)
 
 PLATFORMS