Describe the bug
The default location for Arduino to place the sketchbook is

<UserHome>Documents/Arduino/ 

the default generated by the plugin is

<UserHome>/Arduino/ 

To Reproduce
Steps to reproduce the behavior:

1. Open a standard Arduino install and install a library using the library manager
2. open Sloeber and attempt to use theat library
3. the library is not found, and Sloeber attempts to download it

Expected behavior
I would expect Sloeber to look for libraries and toolchains in the same default directory as Arduino by default

Desktop (please complete the following information):

• Windows 10 Arduino 1.6.x and 1.8.x

Additional context
This is the line that is wrong: