Stick [Context `{Funext}.] inside a section

[Context] is only meant to be used for local assumptions, not axioms.
And this files doesn't import the funext axiom file, so I assume this is
meant to be local.
Merge branch 'funext-not-axiom' of https://github.com/JasonGross/HoTT into JasonGross-funext-not-axiom

Conflicts:
	theories/hit/minus1Trunc.v