[css-values-5] Typo

[cdoublev]

The current definition of the generic interpolation notation requires separating interpolation stops by a whitespace:

[ [ <easing-function> || <segment-options> , ]? <input-position>{1,2} : <output-value> ]*

The comma should also be hoisted between the optional stop options and the stop.

[cdoublev]

I also committed a change that prevents re-ordering the first argument, which is an obvious oversight.

But please make appropriate corrections as you see fit.

[cdoublev]

Replaced a remnant of <progress> with <progress-source>, which is also an obvious oversight.