Add !global flag to stop sass 3.3 warnings

Conflicts:
	dist/core/mixins/_describe.scss
	dist/core/mixins/_it.scss
	dist/core/mixins/_runner.scss
Remove !global from variable declarations
Test only sass 3.3

Conflicts:
	.travis.yml
Interpolate values
Merge pull request #71 from tctcl/sass-3.3

Sass 3.3