DS-2313 - Revert to compiling Mirage2 styles with SASS 3.3.14 for better IE compatibility

https://jira.duraspace.org/browse/DS-2313

Fixes the Internet Explorer 10 or 11 breadcrumb display issue by simply reverting to compiling our CSS files using SASS 3.3.14.  Compiling with SASS 3.3.x seems to work fine with all major browsers (including Internet Explorer).

It seems that 'bootstrap-sass' (which Mirage2 uses) has a minor IE breadcrumb incompatibility with SASS 3.4.x.  I've logged a ticket with the 'bootstrap-sass' team:
* https://github.com/twbs/bootstrap-sass/issues/803

This is all related to a new behavior introduced in SASS 3.4, which is described in much detail in this SASS ticket: https://github.com/sass/sass/issues/1395