Add linebreak in failure text

This is just a suggestion; I know that this change might actually belong in the `snowhouse` repo. I found that adding a line break in the failure message made it easier to visually compare the 'actual' and 'expected' values.

Before:
```
My object has some behavior:
/some/very-long/path/to/the-test.cc:154: Expected: equal to #<value-1>
Actual: #<value-2>
```

After:
```
My object has some behavior:
/some/very-long/path/to/the-test.cc:154: Expected:
equal to #<value-1>
Actual: #<value-2>
```