Local variable types are not updated upon changing context if their name is the same

**Describe the bug**

When you have two contexts with the same local variable name but different data type, the data type is not updated with "up" or "down". Adding a relevant watch expression does trigger an update (at the moment of adding).

**Please complete the following information:**
* OS: Ubuntu 18.04
* gdbgui version (`gdbgui -v`): 0.13.1.1
* gdb version (`gdb -v`):8.1.0.20180409-git
* browser [e.g. chrome, safari]: chrome