Merge branch 'add_gem_lock_to_mime_magic_shim' into 'master'

Add Gemfile.lock to mimemagic shim

See merge request gitlab-org/gitlab!58198

vendor/shims/mimemagic/Gemfile.lock

+PATH
+  remote: .
+  specs:
+    mimemagic (0.3.7)
+
+GEM
+  remote: https://rubygems.org/
+  specs:
+    rake (12.3.3)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  mimemagic!
+  rake (~> 12.0)
+
+BUNDLED WITH
+   2.1.4