Error: build-essentials missing

I get the following error when running `gut`:

``` bash
[localhost] A dependency appear to be missing on localhost: build-essential
```

Looking through the code, this means either `gcc` or `make` is missing. I have both:

``` bash
$ gcc --version
gcc-5 (Homebrew gcc 5.2.0 --without-multilib) 5.2.0
$ make --version
GNU Make 3.81
```

Am I missing something?
