[css-flexbox-1] Wrong comment about `flex` defaults

[felipecrv]

In the table about the flex propery, the initial property is said to be 1 0 auto (https://www.w3.org/TR/css-flexbox-1/#flex-property)

But a comment below says The initial values of the flex components are equivalent to flex: 0 1 auto.

[tabatkins]

As noted in the PR, the correct initial values are equivalent to "flex: 0 1 auto" (but also shorthands don't have initial values, so the spec is wrong in multiple ways right now).

[tabatkins]

And fixed now.