update to spam_2.6-0

public/LICENSE-text.html

public/articles/figures/fig_ch2_factors.png

public/articles/figures/ill.png

public/articles/figures/tree.png

public/articles/index.html

public/articles/jss15.pdf

public/articles/spam.html

public/articles/spam_files/figure-html/disp6-1.png

public/authors.html

public/docsearch.css

public/docsearch.js

public/index.html

public/index_files/figure-html/sparsematrix-1.png

public/link.svg

public/news/index.html

public/pkgdown.css

public/pkgdown.js

public/pkgdown.yml

public/reference/Oral.html

public/reference/UScounties.html