Use the same versions in API::GroupBoards

This ensures that the mentions of GitLab versions in API::GroupBoards
are the same as in CE. Technically this might not be correct if the code
was backported to CE, but there is no harm in using the same code as CE.

lib/api/group_boards.rb

@@ -24,7 +24,7 @@ module API
     resource :groups, requirements: API::NAMESPACE_OR_PROJECT_REQUIREMENTS do
       segment ':id/boards' do
         desc 'Find a group board' do
-          detail 'This feature was introduced in 10.4'
+          detail 'This feature was introduced in 10.6'
           success ::API::Entities::Board
         end
         get '/:board_id' do
@@ -32,7 +32,7 @@ module API
         end
 
         desc 'Get all group boards' do
-          detail 'This feature was introduced in 10.4'
+          detail 'This feature was introduced in 10.6'
           success Entities::Board
         end
         params do
@@ -48,7 +48,7 @@ module API
       end
       segment ':id/boards/:board_id' do
         desc 'Get the lists of a group board' do
-          detail 'Does not include backlog and closed lists. This feature was introduced in 10.4'
+          detail 'Does not include backlog and closed lists. This feature was introduced in 10.6'
           success Entities::List
         end
         params do
@@ -59,7 +59,7 @@ module API
         end
 
         desc 'Get a list of a group board' do
-          detail 'This feature was introduced in 10.4'
+          detail 'This feature was introduced in 10.6'
           success Entities::List
         end
         params do
@@ -70,7 +70,7 @@ module API
         end
 
         desc 'Create a new board list' do
-          detail 'This feature was introduced in 10.4'
+          detail 'This feature was introduced in 10.6'
           success Entities::List
         end
         params do
@@ -85,7 +85,7 @@ module API
         end
 
         desc 'Moves a board list to a new position' do
-          detail 'This feature was introduced in 10.4'
+          detail 'This feature was introduced in 10.6'
           success Entities::List
         end
         params do
@@ -101,7 +101,7 @@ module API
         end
 
         desc 'Delete a board list' do
-          detail 'This feature was introduced in 10.4'
+          detail 'This feature was introduced in 10.6'
           success Entities::List
         end
         params do