Updated docs

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docs/objects/Dropdown/selectItem.md

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+## selectItem
+selects a item in the dropdown (same as a player would click on a item)
+
+#### Parameters: 
+1. `number` The index which should get selected
+
+#### Returns:
+1. `object` The object in use
+
+#### Usage:
+* Creates a default dropdown with 3 entries and selects the second entry.
+```lua
+local mainFrame = basalt.createFrame()
+local aDropdown = mainFrame:addDropdown()
+aDropdown:addItem("1. Entry")
+aDropdown:addItem("2. Entry",colors.yellow)
+aDropdown:addItem("3. Entry",colors.yellow,colors.green)
+aDropdown:selectItem(2)
+```