Bump rake from 10.4.2 to 12.3.3 in /tests/plugin

Bumps [rake](https://github.com/ruby/rake) from 10.4.2 to 12.3.3.
- [Release notes](https://github.com/ruby/rake/releases)
- [Changelog](https://github.com/ruby/rake/blob/master/History.rdoc)
- [Commits](ruby/rake@v10.4.2...v12.3.3)

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

Author: dependabot[bot]

tests/plugin/Gemfile

@@ -1,5 +1,5 @@
 source 'https://rubygems.org'
 
-gem 'rake', '~> 10.4.2'
+gem 'rake', '~> 12.3.3'
 gem 'rspec', '~> 3.4.0'
 gem 'vimrunner', '~> 0.3.1'

tests/plugin/Gemfile.lock

@@ -2,7 +2,7 @@ GEM
   remote: https://rubygems.org/
   specs:
     diff-lcs (1.2.5)
-    rake (10.4.2)
+    rake (12.3.3)
     rspec (3.4.0)
       rspec-core (~> 3.4.0)
       rspec-expectations (~> 3.4.0)
@@ -22,6 +22,6 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
-  rake (~> 10.4.2)
+  rake (~> 12.3.3)
   rspec (~> 3.4.0)
   vimrunner (~> 0.3.1)