revision to New York Aurora headnote

In consultation with Susan, I have revised the final sentence of the headnote for the New York Aurora (Poems in Periodicals) from "Whitman published two poems in the Aurora but left his position as editor by mid-May, following disagreements with the publishers over their efforts to shape his editorials" to "Whitman published two poems in the Aurora but left his position as editor by late April, following disagreements with the publishers over their efforts to shape his editorials." This change more accurately reflects the timeline of Whitman's association with the newspaper as set out in The Journalism and as reflected by the dates of his contributions to the paper.

~Liz