vegandevs/vegan: vegan 2.5-4 released

<strong>vegan</strong> 2.5-4 was released on CRAN. This fixes testing errors in <strong>R-devel</strong> due to changes in <code>formula</code> (issue #299) and errors with new optional tests in <strong>R-devel</strong> (issue #305). Bugs were fixed in <code>decorana</code> (issue #303) and <code>goodness.cca</code> and also documentation glitches (issue #304). Adjusted <em>R</em>&lt;sup&gt;2&lt;/sup&gt; is again enabled in <code>rda</code> and <code>cca</code> (issue #295).