fix(fab): Fix transitions by importing correct mdc-animation resource (…

…#1325)

packages/mdc-fab/_mixins.scss

@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-@import "@material/animation/variables";
+@import "@material/animation/functions";
 @import "@material/elevation/mixins";
 @import "@material/elevation/variables";
 @import "@material/ripple/mixins";