Typo corrected in encyclopedia entry

Archive user Andrew Rosa pointed out a typographical error in the encyclopedia entry for "Leaves of Grass, 1855 Edition," which I have fixed. In the bibliography section, the citation for Ed Folsom's article, "What We're Still Learning about the 1855 Leaves of Grass 150 Years Later," previously read "What We're Still Leaning about the 1855 Leaves of Grass 150 Years Later."

~Liz