Fix rms-set-scales function to make it work with sass 3.4

[karlwnw]

Quoting sass backwards incompatibilty change in 3.4.0: "All variable assignments not at the top level of the document are now local by default. If there’s a global variable with the same name, it won’t be overwritten unless the !global flag is used. For example, $var: value !global will assign to $var globally. This behavior can be detected using feature-exists(global-variable-shadowing)."

@see http://sass-lang.com/documentation/file.SASS_CHANGELOG.html @see http://stackoverflow.com/q/27706643/1026660

[gakimball]

Thanks for the PR :) Could you also update the Gem dependencies to specify Sass 3.4+ and Compass 1.0+?

[karlwnw]

Sure ! Done, I updated the versions.

[gakimball]

Awesome, thank you!