Fallback expression

Would it be possible to add a fallback value function to the plugin? Specifically for that browsers that don't support clamp completely ignore the expression. I suggest a simple `font-size: [value-fallback] `using the first value of the clamp as default. Example: ``` font-size: 42px; // Fallback value font-size: clamp(42px, -6.5915492958px + 9.7183098592vw, 180px); ```