Fixes #15142: Add position: relative; to .dropup for proper placement of menus

dist/css/bootstrap.css

@@ -3401,6 +3401,7 @@ tbody.collapse.in {
   border-right: 4px solid transparent;
   border-left: 4px solid transparent;
 }
+.dropup,
 .dropdown {
   position: relative;
 }

docs/dist/css/bootstrap.css

@@ -3401,6 +3401,7 @@ tbody.collapse.in {
   border-right: 4px solid transparent;
   border-left: 4px solid transparent;
 }
+.dropup,
 .dropdown {
   position: relative;
 }

less/dropdowns.less

@@ -16,6 +16,7 @@
 }
 
 // The dropdown wrapper (div)
+.dropup,
 .dropdown {
   position: relative;
 }