Bump pkg-config from 1.3.9 to 1.4.0 (mastodon#12239)

Bumps [pkg-config](https://github.com/ruby-gnome/pkg-config) from 1.3.9 to 1.4.0.
- [Release notes](https://github.com/ruby-gnome/pkg-config/releases)
- [Changelog](https://github.com/ruby-gnome/pkg-config/blob/master/NEWS)
- [Commits](ruby-gnome/pkg-config@1.3.9...1.4.0)

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

Gemfile

@@ -3,7 +3,7 @@
 source 'https://rubygems.org'
 ruby '>= 2.4.0', '< 2.7.0'
 
-gem 'pkg-config', '~> 1.3'
+gem 'pkg-config', '~> 1.4'
 
 gem 'puma', '~> 4.2'
 gem 'rails', '~> 5.2.3'

Gemfile.lock

@@ -435,7 +435,7 @@ GEM
     pg (1.1.4)
     pghero (2.3.0)
       activerecord (>= 5)
-    pkg-config (1.3.9)
+    pkg-config (1.4.0)
     premailer (1.11.1)
       addressable
       css_parser (>= 1.6.0)
@@ -756,7 +756,7 @@ DEPENDENCIES
   parslet
   pg (~> 1.1)
   pghero (~> 2.3)
-  pkg-config (~> 1.3)
+  pkg-config (~> 1.4)
   posix-spawn!
   premailer-rails
   private_address_check (~> 0.5)