[Bug] reporter minimal doesn't throw "undone tests"

Reporter minimal doesn't throw "undone tests" and so exit with 0 instead of 1.

``` shell
/test (master⚡) ./node_modules/nodeunit/bin/nodeunit --reporter minimal ./tests/my.test.js
my.test.js: ..% /test (master⚡) echo $?
0
/test (master⚡) ./node_modules/nodeunit/bin/nodeunit ./tests/my.test.js

my.test.js
✔ constructor
✔ _getKeywords

FAILURES: Undone tests (or their setups/teardowns):
- onKeywords

To fix this, make sure all tests call test.done()
/test (master⚡) echo $?
1
/test (master⚡)

```