Add modifiers for wider menus

Author: vctrfrnndz

lib/dropdowns/index.styl

@@ -74,6 +74,13 @@ $dropdown-caret-color ?=         #000
   box-shadow 0 6px 12px rgba(0, 0, 0, .175)
   background-clip padding-box
 
+  // Modifiers to make the menu wider
+  .dropdown-menu-md
+    min-width: 175px
+
+  .dropdown-menu-lg
+    min-width: 200px
+
   // Aligns the dropdown menu to right
   //
   // Deprecated as of 3.1.0 in favor of `.dropdown-menu-[dir]`