Issue Type: Bug

Hi,

I have a set of tasks defined for everyday use, the build one being a series of tasks linked via dependsOn. Due to one of the recent builds [don't know if it was today's, I don't think I built anything on friday], tasks with dependsOn are no longer working on my machine.

This simple scenario, for example, fails:

tasks.json

[...]
        {
            "command": "Write-Host 'Second'",
            "dependsOn": "First",
            "group":
            {
                "isDefault": true,
                "kind": "build"
            },
            "label": "Second",
            "type": "shell"
        },
        {
            "command": "Write-Host 'First'",
            "label": "First",
            "type": "shell"
        }
[...]

Running the task Second without dependsOn works and "Second" is correctly outputted. Running with dependsOn errors out with the following Tasks output:

Cannot read property 'type' of undefined

I can verify this still works as intended on 1.24.0. Any guidance here would be appreciated.

VS Code version: Code - Insiders 1.25.0-insider (28d5806, 2018-06-11T05:17:42.700Z)
OS version: Windows_NT x64 10.0.17134