Unable to get auto complete to work in Monodevelop or Visual Studio Code for Unity3D code.

I am unable to get The auto complete drop down list thing to work for Unity3D code in the included Monodevelop, the one from the site 5.10 of Monodevelop, or the Visual Studio Code. I can get all 3 to work perfectly fine for standard C# code though.

Like: If I type "v" it shows Void, but not Vector.

I am using Linux Mint 17.3 Rosa.

Any one know of a way to fix this?