Custom language command never ends

- VS Code Version: 1.30.0
- OS Version: Windows 10
- Code Runner Version: 0.9.5

**Describe the bug**
I added a quick command to compile and run [coconut](http://coconut-lang.org/) files:

```"coconut": "$pythonPath -um coconut -r --target 36 $fullFileName",```

It recognizes the `.coco` files and runs the correct command:

```C:\Users\...\python.exe -um coconut -r --target 36 "e:\code\python\coconut\test.coco"```

And I can see the build and run output in the Output Window. The plugin doesn't seem to know when the command ends, though, and it thinks it's running until I manually "Stop Run Code". Until I do this I cannot run anything else.

If I manually run this command in the terminal window it works as expected.

**To Reproduce**
Steps to reproduce the behavior:

1. pip install coconut
2. add command from above
3. create a `.coco` file
4. Run Code

**Actual behavior**
`[Done]` never appears and I cannot run again until I manually stop it.

**Expected behavior**
The plugin should recognize the end of the run.

**Screenshots**
If applicable, add screenshots to help explain your problem.