core: Lock in plugin install of a specific version

CHANGELOG.md

@@ -57,6 +57,7 @@ IMPROVEMENTS:
 BUG FIXES:
 
   - core: Adding a box from a network share on Windows works again. [GH-3279]
+  - commands/plugin/install: Specific versions are now locked in.
   - commands/rsync-auto: Interrupt exits properly. [GH-3552]
   - commands/rsync-auto: Run properly on Windows. [GH-3547]
   - providers/virtualbox: VirtalBox detection works properly again on

lib/vagrant/plugin/manager.rb

@@ -72,13 +72,6 @@ module Vagrant
           install_lambda.call
         end
 
-        # If the version constraint is just a specific version, don't
-        # store the constraint. However, if it is a prerelease version,
-        # we DO store the constraint to avoid Bundler updating it.
-        if opts[:version] && opts[:version] =~ /^\d/ && opts[:version] !~ /[a-z]/i
-          opts.delete(:version)
-        end
-
         # Add the plugin to the state file
         @user_file.add_plugin(
           result.name,