fix scss test for compass 1.0.0

prior to this change travis fails with
```
FAIL: test_compass_import (static_precompiler.tests.test_scss.SCSSTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/travis/build/sir-sigurd/django-static-precompiler/static_precompiler/tests/test_scss.py", line 230, in test_compass_import
".round-corners {\n -webkit-border-radius: 4px 4px;\n -moz-border-radius: 4px / 4px;\n border-radius: 4px / 4px; }\n"
AssertionError: '.round-corners {\n -moz-border-radius: 4px / 4px;\n -webkit-border-radius: 4p [truncated]... != '.round-corners {\n -webkit-border-radius: 4px 4px;\n -moz-border-radius: 4px [truncated]...
.round-corners {
+ -webkit-border-radius: 4px 4px;
-moz-border-radius: 4px / 4px;
- -webkit-border-radius: 4px 4px;
border-radius: 4px / 4px; }
```