Auto merge of servo#82 - metajack:release-0.3.4, r=SimonSapin

Bump version number for release.

r? @SimonSapin

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Remove some default associated types, so that default methods don’t h…

…ave to be overridden.

Since rust-lang/rust#26728 , Servo would get build errors like:

    error: the following trait items need to be reimplemented as `AtRule` was overridden: `rule_without_block` [E0399]
        type AtRule = CSSRule;
        ^~~~~~~~~~~~~~~~~~~~~~

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